Need Cable recommendation for VAC/Avalon Combo.

I've had good luck with Synergistic Research actively shielded cabling.

I have owned the FS preamp, but the Presence Delux 2, and Avalon Eclipse speakers. I have heard Vac Rennaissance amps for extended periods on two different occasions. I own K-S Emotion, and still run it through my system. FWIW , I own the Vac Phi 300.1, and they do not have the inherent body and texture that the Rennaisance 300b amps have. Call it coloration, or what have you. So, you are definitely getting depth and body from the amps. I did feel the FS PD 2 did not ad any colorations, quite neutral IMO. You could try a another cable. It would be the easiest experiment, but the K-S is very good.It is a tad warm perhaps, but lets all the detail through. Here's a curveball. See if you can try a Shindo preamp. I am just not familiar with the Avalon Eidolon Diamond, but I understand it is one of the best out there.

I run Phi 300.1's but with the Ren Sig II pre...I use KCI Silkworm SE in my system and they have withstood many challengers at a variety of price points. John at KCI has a demo policy on Silkworm's (not the SE as they are custom gauge) I would encourage you to demo them from him and listen for yourself to see if it's what you seek, but my experience has been exceptional synergy with VAC gear...

Very nice system. I have seen MIT cables used with large Avalon speakers (the latest version of the Eidolon Diamonds) and large Pass tube amplifiers and they worked extremely well together. I believe the cables were MIT Magnum M3 or M2.