Glai, very interesting amps of choice indeed. I actually use to own the same Avalons which were set-up in my main designated room. Associated gear was ARC Ref3, Arc Ref300 MK2's, I also had VTL Sig 450's with the 7.5 pre original not MK2 version and preferred VTL 450's and ARC Ref3 combo.
Three of the amps you mentioned, Cat., Vac. and Lamm are all on my short list and want to hear in in my current set-up to compare with what I currently have, this set-up is not in my designated room but a secondary set-up. I am currently using Pass X-600.5 with ARC Ref3 and really enjoying it. I have been told that the REF3 will match nicely with the Lamm but unfortunately no so good with the Cat or Vac so if and when I go that route unfortunately I will be looking at pre's to match the amps. Regarding the VAC 300.1 realistically you are likely looking at two of them along with the Vac Sig. Pre which is allot of money. I have been told that the Cat. sounds marvelous and you will save allot of money going this route but again you should be looking at their pre as I have heard from others the Ref3 is not a good match.
A dealer close to me just got a VAC 300.1 and Sig. Pre so I'm anxiously awaiting for them to be broken-in so I can hear them.
Keep me updated regarding your outcome and if you choose to either get a Cat or Vac's let me know as I'm also looking at one of these.