I think the impressions you may have read about the Beyers were probably regarding the DT880's. They are very nice but, as you said, particularly bass shy. That said, the DT990's are similar to the 880's but with more bass. I have a pair of both and I can say that the Crack brings out much more bass in both Beyers than I'm used to hearing with them. Personally, with the Crack, I think the 990's have too much bass (I actually keep these cans for late night home theater sessions).
The Senn. 600/650 are a little laid back but the right amp can make a huge difference. Unfortunately, I sold my 600's not too long ago. The 650's have more bass than the 600's and there's lots of fans of the 580 too (I've never owned them so I won't comment).
I think that many of the AKG's will work with the Crack with the exception of the 701/2 or 340 electrostatic/dynamic hybrid. One of my favorite cans for classical is the K501. They too are a little bass shy but they might shine on this amp.
As you can see, there's a ton of choices (and I haven't even mentioned Ultrasones, Sonys, or Audio Technicas). But, that's one of the cool things about headphones. You can try a pair for a little while and resell them without much of a loss. If I'm curious about a particular model, I check out the Headfi "for sale" forum and buy them used. I've never gotten a bad pair that way. If they aren't my cup of tea, I put them up for sale again and just loose out on the shipping.
Also, Headfi has local meets all over the world. This will give you the opportunity to spend some time with some phones on other folk's systems.
In fact, if you're in the Chicago area, the International Meet is going to be there the first weekend of June.
All in all though, unless there's a meet in your neck of the woods in the next week or two, if I was in your shoes, I'd just buy a used pair and live with it for a little while.
