So I'm down to two players now, they are the more knowledgeable ones concerning fluff and they're going to be going for a BA Librarian and Salamanders Techmarine team. I'm wondering if I should adjust their encounters so they don't get too overwhelmed.

Has anyone else here gm'ed for only 2 players before and have any advice?

I'm not a big fan of giving players multiple characters to run, but in this case you might want to consider 2 PCs per player (an Apothecary and an Assault or Tactical Marine would be very useful additions to your current build). DW is designed around squads , after all...

Thats what I'm thinking right now. But I might make one for each of them that will force them to role play, I'd let them choose the specialty but I'd pick a chapter for them. One of them is going to be an Iron Hand and there will be difficulty between him and the Salamander.

Another question, has anyone ever utilized Dark Eldar in DW? I've looked through the Only War information on them and most of their weapons are... lacking, and probably will not cause much harm to Space Marines. The Incubi seem like the most capable of dealing actual damage.

They'd be ambushing the kill-team after their Stormraven crash lands on some random planet. JUST AS PLANNED.

Another question, has anyone ever utilized Dark Eldar in DW?

I've used Dark Eldar from the Rogue Trader adventure/supplement The Soul Reaver against Rank 2 DW Marines. I posted my assessment of their performance here .

Another question, has anyone ever utilized Dark Eldar in DW?

I've used Dark Eldar from the Rogue Trader adventure/supplement The Soul Reaver against Rank 2 DW Marines. I posted my assessment of their performance here .

That is very helpful, especially regarding the splinter rifles. I am planning on using Only War entries, and not any hordes really. I will probably revert their unnatural characteristic bonuses to x2 to match them up more evenly with the kill-team. They are also rank 2, so I think it will play out well for them.

_{Some time has passed - how did it go with the dark eldar? I am figuring that any use of them would have to include vehicles, as they primarily seem to spend their time flying around on them and pestering people with those grapple hook things.}

_{As to the topic, I`ve just finished the last of the scenarios in Jericho reach with my players and I`ve had lots of opportunities to test out various monsters and foes, with a variety of results. What I would say is that the biggest factor in my games has been the presence of our iron hands techmarine player, whose ability to resist incoming damage has seem him shrug off attacks that would have killed the other party members twice over. He also dishes out a fair bit of hurt with that servo arm of his and each combat tends to see some opponents being mangled in its steely jaws.}

_{I`m of the opinion that the techmarine, as written, especially if an iron hand, is easily worth two of any other class on the table. Its ability to deal out massive armour ignoring damage and its formidable ability to soak up hurt are a complete game changer. An entire party of them would be unstoppable. No other class combines such a formidable offense with such a strong and reliable defence.}

_{In terms of balancing the threat of a scenario, having such a character can be a major obstacle. Hits that it would shrug off will drop another character and foes that may challenge the party will quickly get tied up and taken down by that character alone. It strikes me as a little strange that techmarines are the most powerful and versatile fighters of the team.....why have any other sort of marine in the party at all?}

_{Some time has passed - how did it go with the dark eldar? I am figuring that any use of them would have to include vehicles, as they primarily seem to spend their time flying around on them and pestering people with those grapple hook things.}

_{As to the topic, I`ve just finished the last of the scenarios in Jericho reach with my players and I`ve had lots of opportunities to test out various monsters and foes, with a variety of results. What I would say is that the biggest factor in my games has been the presence of our iron hands techmarine player, whose ability to resist incoming damage has seem him shrug off attacks that would have killed the other party members twice over. He also dishes out a fair bit of hurt with that servo arm of his and each combat tends to see some opponents being mangled in its steely jaws.}

_{I`m of the opinion that the techmarine, as written, especially if an iron hand, is easily worth two of any other class on the table. Its ability to deal out massive armour ignoring damage and its formidable ability to soak up hurt are a complete game changer. An entire party of them would be unstoppable. No other class combines such a formidable offense with such a strong and reliable defence.}

_{In terms of balancing the threat of a scenario, having such a character can be a major obstacle. Hits that it would shrug off will drop another character and foes that may challenge the party will quickly get tied up and taken down by that character alone. It strikes me as a little strange that techmarines are the most powerful and versatile fighters of the team.....why have any other sort of marine in the party at all?}

Luckily I have an Iron Hands Techmarine, AND a Sons of Medusa Apothecary on the team, both have 4 levels in the flesh is weak and will be very hard to take down.

I haven't done the actualy Dark Eldar mission yet but I tested out how they would fare against a space marine, and I had a new player try out fighting a few with his Librarian. Incubus seem to be the best at combating a space marine in melee combat, though they lack the durability in stats, they have a solid 8 AP on all locations and a weapon that can penetrate armor and do some damage.

To tie them up I'll be using Mandrakes, who will probably be able to get a surprise attack on my players, and although they won't do much damage (their fire-ball attack is somewhat effective), they are really good at distracting and tying up space marines and can escape from combat with their ability.

I will most likely use a Pain engine and a few grotesques as well. With Kabalite Trueborn sniping and laying down ranged weapon fire.

Your point on tech-marines is also very good, they start off with a ridiculously powerful melee-weapon, but I find that their potential in melee-combat is somewhat limited since in most cases they won't be able to get multiple attacks, which I find to be important on melee focused characters. Although a Space-Wolf Iron-Priest or Dark Angels Techmarine would be able to get swift attack through a deed. Furious assault would help with this problem as well. But I have come to the conclusion that Techmarines are the tankiest specialty, even for a space-marine, especially with a lot of cybernetics to add to their TB. Once they have a servo-harness with its ranged weapons they can be pretty adaptable in ranged combat.

Iron Hands and their succesors are arguably the best choice of chapter for Techmarines. And I would allow my players to take the Chaplain Advanced specialty if they are an Iron Hand to become an Iron-Father.