I have a vac phi 200 using audio physics virgos 25 speakers and I find the kt 88's that kevin uses with his amps are very good but the biggest improvement comes from the changing of his 6 sn7 front line tubes.I have 3 sets that I change around from time to time.a 50 year old set of brimar a 40 yr old set of sylvania and a set of rca red base 5692 about 70 yr old military tubes