What trouble did you have with the TRL GT 400 and how did it fair with the AS 200?
Glory
I had problems with it running away, super heating, trashing tubes and blowing resistors. This happened more times than I can count. I think this amp was out of spec, delivering too much voltage for the tubes it was supplied with.
Performance wise Tube Research was wonderful, better than the (then) Atma-Sphere and maybe better in the midrange than the VTL. Since that time Atma-Sphere has upgraded several times and I hope to someday try them again.
As for output volume and reserve power the Atma-Sphere was right in there with the Tube Research but VTL 750 is top dog for dynamics, hard hitting bass and reserve power on difficult material.
Ultimately the VTL 750 is the most reliable tube amp I've ever encountered. One pair of 750s on my Dali Megaline are the exact amps purchased back in 2003 for my Sound-Lab Ultimate. I bought these used and have pushed them for an additional eight years with no repairs !
The second set of VTL I purchased used in 2004 or 2005, I have one of them in the shop right now, first repair in 6 years.
I have replaced tubes several times but when a tube shorts with VTL 750 it takes out a big fuse. Replace fuse, replace tube and repair is done.
Maybe I'm getting old but I just don't deal well with product that fails a lot. I get so depressed I can't enjoy the music.