I think the new BAT equipment is superior to the Ref 600s in every way execpt soundstage and ultimate power. The REF 600 MKI & MKII are very thin sounding, tonally inaccurate, hotter than a radiator with bloated bass as well as a huge noisefloor. They are also incredibly expensive in terms of tube replacement (short life tubes as well). They throw one of the biggest soundstages I have ever heard, and have an iron grip on notes. But, all in all I did not think it was worth ever owning them. The BATS, on the other hand, are dead quiet (comprable to ML & Krell in that respect), with exceptional tonality, detailed bass, beautiful mids and highs and great detail.
The VTLs are very good but you have to get the new ones with the latest revisions. If you get the newest VTL 750 Reference amps, they should do fine. The problem is that you are still dealing with a short life 6550c that costs quite a bit to replace.
If you want something speacial, go to the VK-75SE's or VK-150SE's. They are a huge difference over your current VK-60.
Let me know if I can be of any other help.
Good luck!
Jonathan