TTC,
Probably not a good thing for your wallet that you're keeping your options open!!! This place will eat your wallet alive....and the seat of your pants....quite possibly your backside too!!!
Recently, there have been some reviews of the SuperMono with the SR-71 and PIMETA, and it seems to me that although differences exist, much depends on the kinds of equipment and configurations used. Howvere, I think the alternatives to the SuperMOno are slightly preferred.
What I do think is that there is some possibility (maybe mostly in the ears of the aduitory holder!) that there is a difference between these amps and say $300 and up and those of a lesser cost. (I'll probably get killed for that comment!) Now, I have a SuperDual which is really good for me, but not quite as good as JMT's PIMETA (but mine is only transportable).
In my limited and relatively young experience in all this, I have found Xin's products to be of excellent quality for the price, but I know there are many really good amp products out there, especially from DIYers. You're lucky to have such a good set of products to choosed from, and you're equally inlucky in having to make a choice!!!
If only there was a way for you to try these out before you decide!