I don't have the Insight back yet. But in my studio, I have the luxury of owning 2 1/2 AVA systems. The first is the OmegaStar EC preamp powering the 260EX amp, powering some Paradigm Studio 40v.3's. The second system is the T8 powering the 170EX and that is running my very sweet Dynaco A25XL's. Then the Ultimate 70 proto-type sits next to it all and likes to be hooked up to the Dynaco A25XL's and the OmegaStar EC.
In the studio, I've been able to mix and match 3 amps with 3 sets of speakers and 2 sets of preamps. I think that gives me 18 different possible combinations! When I paired everything up, my goal was biggest soundstage, biggest 3D image and best freq/bass performance. I soon realized that it wasn't just an amp or a preamp or even speakers that controlled the sound of the system. There were some combinations that I didn't like as well. IMO, an all tube amp probably shouldn't be paired whit an all tube power amp. I thinks it gets to0 soft and too slow. Don't confuse this with the hybrids, however. That is a different untest story for me.
The 170EX can really put out a sound stage. It is very musical. Sometimes I think it lacks a little bass, but then I put something else on and wow, there's plenty of bass. The 260EX is very 3D. I can sit at my computer (way to the right) and here faily good stereo and I'm almost out of the triangle. That is incredible IMHO. The U70 blooms. It can't rock the foundation (only 33 watts per channel) but with the right efficiency speaker, that won't really matter, it can play loud enough for most. Don't pair it up with something 84db and then expect it to crack plaster, that's just plain not reality. If you like classical music at moderate levels, sit back and enjoy.
From my point of view, it's impossible to be objective with you on the sound of a particular piece as it just doesn't work that way. That's why I think it's very important to match the amp with a similar and compatible preamp, which in my mind, I have done.
I think I will hook up the U70 to the PAT-4 and see what that is like, a little later this afternoon.
Wayner