Feel free to keep contributing to the thread, it has been interesting even if I'm still clueless. :)
Edit: For what it's worth, I did some listening tonight, A-B'ing with my ATH-M50s. I love the M50s, and if they didn't clamp so tightly I could listen to them all day at work. Going from T1 to M50, there was a massive volume increase which is to be expected, but even when I raised the T1 volume to compensate, they didn't have anywhere as near much slam or impact. The soundstage and detail of the T1 was much better, but they were less exciting than the M50s (which I do consider relatively neutral). I am getting more and more sure by the minute that this receiver isn't able to drive the T1s sufficiently. I'm all for neutral presentation, but it has to have some balls surely. I'm moving house soon, but in the next few months, I'm sure a Bottlehead is on the cards. If that doesn't do it for me, I'll sell them both and buy some high-end Grados. ;)
I am no expert here, but have had T1s for some time now and tried them with a few sources.
From my experience, T1s are pretty amp picky when it comes to amps. It may be driven to very high sound levels by pretty much anything, but that does not mean they are well driven then (sd you have already noticed too).
You have finally done the right thing and tested your equipment and compared to M50s.
Now, for your thoughts about both:
If you are looking for the same bass slam on T1s that you are getting on M50s; you got the wrong headphones. T1s are, IMO, and you will not get the slam that M50s give you. They will have very goo and tight bass with the right amp like WA2 or CSP-2, but for that you need another $1000. Even with those amps, though, it will not be as bass heave as M50s, they are not very neutral from what I understand, more bass-centric.
If you really want to get high-end headphones with bass slam, sell T1s and buy LCD-2s. You will still need an amp. A good one.