This has likely been discussed many times, but can someone point me in the right direction for expanded explanations on using the Dark Heresy powers with the Rogue Trader (and now Deathwatch) psychic power rules? I'm debating on which one to use. The Ascension book kind of merges them but not exactly, which looks pretty good.

Did you ever get info on this? I am wondering what I'd like to do..I think they both work, but all the new games are using the newer method. Does that mean DH isn't what is envisioned for future games...? I'd just like to invest time into the right ruleset.

The DH rules were written by Black Industires, not FFG. Since aquiring the rights to the game FFG have been modifying it how they wan it to function. The original psyker system is something FFG dont seem to like (probably because it is a dice pool mechanic in a d% based game) and have been changing with each newer game.

From the looks of Black Crusade it looks like the WP test method is going to be with us a while, which is a bit of a shame because the overbleed mechanic in the dice pool system although prone to being vastly overpowered is really cool and represents a more experianced psykers ability to be able to push thier powers further.

I would advise being very cautious in mixing the rule sets of DH, RT and DW together, although all based on the same underlying mechanics and very similar rules, they do not balance well together at all.

You can leave DH rules the same for the DH characters.

Reason being, Astropaths in RT are soul-bonded to the Emperor and can there fore use their powers more safely

I use them independently.

Astropaths use one flavor of techniques to put the warp to use, Imperial Psykers use another system. Each with its own up- and downsides. Just like what Space Marine Librarians, Ork Wyrdboyz or Eldar Farseers do doesnt need to be all one interchangeable, compatible system. Or rather it definitly is not, as all those traditions are much too different.