>>If I understand you correctly, you are saying to experiment with amps, presumably good SET's, and determine if this is the correct path for me?<<
I think a subset of high-quality SET amps -- particularly 845 based -- are ideal for Definition systems, but you already have a very fine amp in the Atmashpere OTL so you should begin with that; get accustomed to the combination and see how it satisfies you. Once you have that baseline, then try Audion, Sophia or maybe Melody or Consonance 845 SET amps if you find you still have the appetite for trial.
>>From what I have read, I think the Audion may be closest to what I'm looking for, IF SET is what I'm looking for. Does that make sense? Are there any distributors in the US that would allow an in-home audition?<<
The US importer/distributor for Audion is Gary Alpern, reachable at his web site, http://www.trueaudiophile.com. The unfortunate state of high end audio retail is such that the usual burden is on the prospective buyer to find a way to hear the gear they are interested in, or find home trials from online sources. I don't know where you live nor how far one of Gary's retailers is from you, but start by asking him.
Phil