preamp for Ayre/S805

My current chain is:
Cary 306 -> VTL 2.5 -> Ayre V-5x -> B&W S805.

I'm looking for suggestions for an upward move in preamp; perhaps something fully balanced, as the Ayre is said to sound better that way. I prefer my sound slightly shaded towards the warm side, but not at the expense of low level detail or soundstaging. Budget is in the neighborhood of $3k (used). What are my best bets for synergy here?
I would replace the VTL 2.5 with an Ayre K-5x. I've had both and the Ayre is far superor in bottom end, transparency, soundstage and dynamics. It is also beautifully built.
Also consider the Pass X1, another notch up.