Audio Research VT80SE amp vs Prima Luna EVO 400 or 300

Balanced only.  It’s a fully balanced amp, and you might want to give that issue a think.  Not sure how it would like single ended outputs adapted to XLR from an unbalanced pre.  Evo from what I recall is unbalanced (even with the XLR input options).  

OP — I went from a Prima Luna HP Dialogue Premium integrated to an ARC 160S amp and REF 6SE preamp.  Never regretted that.  I concede it’s not a fair comparison to start with, but I still use my PL in another room and I’ve obviously made my own mental comparisons (room differences and associated equipment, again, make it an unfair comparison).  Subject to all those caveats: I prefer the ARC house sound.  Clear, liquid, bloomy, transparent, just the right dose of fleshiness.  Not even remotely syrupy or rolled off.  In fact I hesitate to even put those words in the same paragraph as “ARC.” Grip and authority might only be a B+ to a bunch of A+ attributes, but those weren’t high points for the PL, either.  When I went from an earlier tube integrated to the PL, the PL seemed awfully neutral for a tube amp.  A smidge chilly.  Sometimes not the kind of neutral I wanted.  Sometimes fantastic.  But in a battle between my mood and the amp, my mood always won.  So I tried SS for a year (BHK monos with BHK pre — yes, yes, I know they have tubes on the input stage, but that’s not relevant here).  Popped the PL back in and remembered that it does create that dimensionality-plus, levitating sound you only get from tubes.  Intent on a return to tubes, ARC entered my scene and I was smitten.  Fell hard for that sound and added a REF40 / REF75SE / Harbeth 30.2 system in my office.  ARC stuff can win over my ears even when they’re in a bad mood.  That was 18 months ago, so time may change my views.  YMMV.  

Flame — hard to say.  Different rooms and very different speakers.  Some time ago when I replaced the 75SE with the 160S, in the same room and system, paired with DAWs, the 160S brought dynamics and “jump factor" to a whole new level.  It is dynamic as hell.  Spanish Moon from Waiting for Columbus became a thrilling ride; air drumming is an involuntary (if mildly embarrassing) response.  The 160S also brought a different sense of clarity/definition.  I hesitate to say better, but different.  More forward.  If you get off on the arresting transparency of a perfect Julie London or Nat Cole recording, or you want to feel the breathiness of Ben Webster, I’ve heard nothing better.  But I think in 10-20 years some will still love the 75SE for its ability to remain unnoticed, its naturalness, and its relaxed presentation.  In real life, when someone is playing a piano or guitar in your room, they are not trying to impress you with sonic charms.  Such is the sound of the 75SE.  In fact, it is VERY good in this regard.  But a true confession: I waffle between my teenage brain seeking punch and sizzle, to a more adult appetite for effortlessness and flow.  For example, at least once a month I seriously consider auditioning a D’Agostino stereo amp in place of the 75SE.  The 160S also offers more punch, with a noticeable "charm" in that lovely lower midrange, upper bass region.  And good ole’ bass is definitely tighter and more pronounced.  Final word on all this: the ARC break-in period is notoriously long, and it’s not malarkey.  Make sure you’re listening to a fully broken-in ARC amp, otherwise all bets are off.  

@BIF,

Ken Kessler thinks the REF 75SE is the best amp they ever made, current lineup included.  And he literally compiled/authored the latest book about ARC.  So, no, I would not agree with the marketer's notion that the 160S blows away the 150SE or the 75SE.  My ears, and my reading, tell me that ARC has moved 1-2 degrees away from their traditional sound to add a bit of what my teenage ears liked.  But just a smidge.  Then you have flat-out improvements with capacitors, resistors, wiring, etc.  I wouldn't have moved to the 160S in my trophy system if I didn't like it more.  I'll just say this: if they come out with a 260S, I would trade up and sacrifice the 160S for the new toy.  But I will never sell my REF 75SE (or REF40).
And good call on the KT150s for OP.  My 75 always had them, as has the 160S.  But I played around with the EL34s v the KT150s in my PL.  In that amp, I preferred the EL34s (they softened some leading edges, which you can understand me liking from my first note).  But talk about oranges to apples ... the ARC amps that can accommodate KT150s all benefit from that swap, I believe it's fair to say without controversy. 

Lastly, seeing the note about biasing, it's easy on the 75SE.  Child's play.  And gives you one more thing to monitor and kid yourself into thinking you're a participant ...