Modwright KWA 150

I'm biamping with 150's, though probably don't need to be with my current speakers. I also used a single 150 for a year before going with two. I would not define "warm" as bass heavy, but rather having a bump in the lower mids. That said, I would say the KWA150's err closer to the side of neutral, but definitely do have a very natural and magical midrange, and perhaps there is a slight bump there, but I would not go as far as calling them "warm". They certainly are not cool or analytical either. "Natural" comes to mind when I think of them. If you prefer warmth you might want to look into the KWA 100SE, where I don't have experience to convey (see 6moons review of that amp). Back to the 150; Bass has plenty of authority, even more so biamped, but not lacking at all with one. Right now I'm using speakers with internal amps for the bass section so it's not making much difference for me personally, but before this I had Coincident speakers that really benefited from the KWA's bass prowess. The extension at both ends is smooth and seamless. They are wonderful amps. Read the reviews on 6moons and in TAS (Golden Ear winner), as well as on the AudioCircle Modwright section. Disclaimer: Dan is a client of mine, but I've used his products long before he became a client. Hope that helps.

I would say the KWA150 is pretty darn neutral. Though other system changes do not allow me to make a definitive statement, compared to my ARC LS26/SD135 combination, the Modwright LS36.5/KWA150 present a slightly more neutral balance through the midrange, with much better low frequency definition and more extended and natural highs. I'm not sure I agree with many of the comments on this amp that it sounds "tubelike". It does resolve spatial information very nicely and does exhibit a very natural tone that reminds one of tube gear. But, on balance what I hear in my system is solid state done very, very right--an absence of grain, natural tonality and good spatial cues combined with awesome power, authority and extension at both extremes. What do you intend to drive with the amp?

Looking into speakers at the moment...
Maybe Legacy Focus HD or Audio Physics Tempo 25's or Wilson Benesch Curve or Martern Miles III

Would you say vocals are very natural sounding or do they come through with some colouration?

I have been using a Moon i-3 but its time to move up to pre/power as it does not have grunt I need.

Ideally, you would want to make a decision on your speakers in conjunction with that of your amplification. I'd narrow down my speaker options to your top contender and then try different amplification to see if you can obtain the sound qualities you are looking for. Though I have not heard them all, the speaker choices you have listed are quite different sounding. Picking an amp without knowing which speaker you will likely pair it with may not get you where you want to go.