Floosh, yeah I've had an initial foray into amp experimentation. I have an Onix SP3 playing for the past two weeks. It has the recommended upgraded tubes - Groove Tubes 12AX7, Electro Harmonix 6922, SED Flying C 6L6GC.
My other amp I had been using is the Dayens Ampino 25WPC integrated. So now I'm using a dynamic ~40WPC push pull tube amp. I find the SP3 to have more soundstage depth, better fleshiness of instruments, isn't less detailed than the Ampino, but takes a little of the edge off. Overall, I think an improvement, but I haven't yet swapped back to the Ampino again. I want to do that again sometime soon after my ears have really settled into the SP3, as I've found sometimes when I swap back I find things I didn't realize I was missing after the newness of the new amp wears off.
I'm quite interested in trying the new Red Wine Audio Signature 15 - it might be the best of both worlds and would save me from focusing next on cleaning up power to amp/preamp, allowing me to focus on cleaning up the power on my source.