Anyone own 200iq and prefer kt150 over kt88

Also on phono stage - realize you're already running a 100 Watts/ch tube power amp that will throw out several times the heat of a typical tube phono stage...and you're concerned about heat from the phono stage in that scenario?? 

The VAC Ren phono stages use a sextet of 12ax7 tubes, which just don't throw out much heat. I can't see it ever being a concern. Stages that use 12au7 (yuck) or 6922, add a little bit more heat. But you'd need a stage chok-full of 6N30 like the ARC Ref 3 before it will approach (or exceed) the heat of a tube power amp.

No, the KT150 were pretty awful in my 200iQ monos - killer slam and weight but completely lacking everywhere else. They can hardly even last 5 minutes of listening before I have to yank ’em out and get some sonic relief. I feel like I wasted time & money trying them.

But I actually like the Tung-Sol KT120 a lot, and even slightly prefer them to stock KT88 Gold Lion most of the time. But it’s a close call, and I see why many prefer the KT88.

I use the VAC Renaissance SE phono stage and it’s amazing. I also auditioned it in non-SE form and that’s fantastic too. Don’t feel like you HAVE to do the SE upgrade (the non-SE is even possibly, maybe, a little warmer and more romantic sounding). My only critique is you might not love the built-in Lundahl SUTs but I have my own SUT collection so that was never a problem (I even prefer a Bob’s Devices 1131 or Sky to the Lundahl LL1931). System is vinyl only!

And I agree with others - if you want to run KT150, get an amp designed especially for them!

I've found KT150s perform their best in amps truly designed to run them natively at their optimum operating rage.  

My current mono KT150 amps run higher plate voltage, with 25% larger transformers, as compared to all of my prior amps with EL34, KT88, KT120s.   

Tried KT150s in my smaller amps with lower plate voltage(s), and KT88s were better.  KT150s sound different and better in the amps designed for them.  It's a different sound, stage, tone, musicality in purpose built amps vs just plugging them into a socket that will fit them.    

Can't help on the first question, I just use KT88s in my Phi 200 and am happy with them so I'm not trying any other output tubes (you could try getting some different input tubes, I like NOS RCAs for their richness, but you could get NOS Sylvanias for a leaner sound). 

On your second question, I have both a tubed phono stage (in my Shindo preamp) and a solid state phono stage (a prototype of the current Merrill Audio Jens phono stage made for me by its designer).  The Shindo is very quiet and very good in all respects, but the solid state unit is dead quiet, a bit more dynamic, has more loading options and seems to make instruments and voices come alive.  I could happily live with either, but I generally use the solid state, though, as it is (IMHO) an extraordinary unit..