Oh, wow. There's a LOT of audio out there. Besides the awesomeness that is Six, what are your favorite subjects?
And when I saw a lot, I mean Big Finish alone has well over 200 titles available, not just with the Doctors but with Iris, Gallifrey has its own three-season miniseries, Daleks, Davros, Cybermen, and Sarah Jane has her own spin-off audio series that's 9 cds long.
Hmmm. I'm going to suggest an earlier title called Spare Parts. It's not a Six, but that's ok. It's Five, and an adventure on Mondas, which if you're a fan of the Cybermen, you'll recognize straight away.
There are a couple on here who have all of the titles and could give you everything you could possibly want to know about them. It might help them if you narrow down what stories you enjoyed, then they can suggest audios that are similar.