Auditioning amplifier gear: simultaneous auditions, online retailers you trust?

Hi folks,
I'm in the process of choosing speakers and amps. First, I get the speakers and try them out against another pair I'll buy here in Denver. Then, I'll return the pair I like least.

The next stage is to choose an amp which has the right character and power for the speakers I choose. I've never owned a truly hi-fi amp. state or solid state.

Some parameters:
* purpose is two-channel music listening
* budget $3k max; be nice to hit below that, say $1.5k
* exploring whether to go separates or integrated, hybrid tube/solid
* preliminary brands which have caught my eye: PS Audio, Schiit, Parasound, Rogue, Vincent, Peachtree
* present stable of gear (vintage): Adcom separates (535L 60w/ch. with GTP 400 preamp), Rotel RX-830 receiver (20w/ch)

QUESTION: My question is about how to narrow down choices. Some gear I can audition locally. Other stuff, I'll need to buy on the internet. So, some questions.

1. Hybrid/Solid State — Do you think I'll get a good basic sense for "tubes vs. solid state" by listening to any decent tube and any comparable solid state? For example, let's say I'm interested in Vincent vs. PS Audio but can only compare, say, Rogue vs. Parasound. I know these amps will have their own signature, but will I at least glean the basic difference between tubes/non-tubes?

2. Number of simultaneous comparisons. How much gear have you profitably compared at once? I am thinking I'll try 2 at once. I could put three on my card but then it starts to feel a bit ridiculous. Or maybe not?

3. Which internet retailers do you trust. I've seen good comments on Audio Advisor and Music Direct, mixed comments on Upscale Audio, Uptown Audio. If I were to have some gear from online dealers for a trial, who would be good?

Advice appreciated, including any direction to previous threads about this topic. I do search before posting my questions, but there's a lot of threads and some are old or not quite relevant to my question.