How would you characterize the VAC tube amps?

upper vacs and pass amps are creme de la creme of each type of amplifier (among a handful of others of course)

i would agree that vacs will provide more expansive imaging as well as ’bloom’ in the midrange and upper bass, and less attack and solidity on deep bass

vac amps in my opinion do not roll off the highs much, may sound prettly close to pass in that range

@chungjh,
I’d call Wayne at Pass. Two things still come to mind. Re-check bias on your Pass amps, re: slow warmup. Some do get sent back and get re-checked after some run-in time. Concerned for you that your SL 545s might suffer with any lower power tube amps. I run capable 120w KT150 mono tube amps with larger transformers myself, and I’ve heard your same speakers with my 120w tube amps. As I recall it was still on the edge of being "just enough", maybe.   I still wonder if your preamp is not driving the amps well enough. Separate topic, ask Wayne. Read this article to refresh thoughts about the type of amplification to make the 545s sing.  

This review reminds me of a few things to pass along about "power" vs. current for your 545s. https://www.dagogo.com/sound-lab-ultimate-545-electrostatic-loudspeakers-review/2/
Quote:
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(At 86dB efficiency with an 8-ohm impedance, the U-545 needed more wattage than current in amplification, so a high-output Class AB would be more appropriate generally. But the XA200.8 is Pass Labs’ most powerful Class A monoblocks in its ‘High Current’ series, occupying only two chassis and second-in-line to the company’s four-chassis, $85k Class A Xs 300, therefore provided the necessary wattages in high-current drive and propelled the panels to enormous scale and performance)

Anyone with experience with VAC phi 200 or 200iq?

I don't think VAC amps can be characterized with a house sound, as sound from their 300B based Renaissance amps (30/30, 70/70) is very different from the KT88 based Phi 200.  

The VAC Phi 200 has very robust bass, but lacks transparency, air and sweetness of their old Renaissance series amps.  

Additional brands you may want to consider:  Air Tight, Quicksilver, Music Reference and Manley