I've played against a few 6 tie swarms before, and I think maybe even a 7 tie swarm when I was new to the game, but never a 8 tie swarm until today at my local game store.
I have to say, it's definitely a very intimidating sight at first.
I debated about what type of squad to make to go against it, but to save time and make it simple I just flew my best 4 ship rebel squad (X,X,B,HWK), even though it's not the most ideal for a large swarm like that.
Well to my surprise I ended up winning. In the end it came down to Wedge with 3 hull and 1 shield left versus an obsidian tie with 2 hull left. After dancing around the board a bit we finally got in range and I took him down.
The thing that worked to my advantage was my opponent had only flown an 8 tie swarm a few times before, so he had trouble keeping them together. He lost a lot of actions, and often had several ships that couldn't shoot at me each round. That allowed me to take minimal damage while taking down 1 or 2 of his ships each round.
His luckiest break was when he had a tie at range 1 shoot at my hwk with 4 hull left and get 1 hit and 2 crits. I got only 1 evade, and my 2 crits were both direct hits.