Get the M60s and open the windows, heat be damned. I've had'em for 10 full years and this heat thing is overstated in my lengthy experience. Well within your stated budget used and a wonderful company to deal with and always available. These comments are in no way meant to disparage the makers of the other fine products you've listed. BTW, I live just outside New Orleans...we invented hot and muggy.
Keep in mind that every time you double the wattage, you go up 3db. It takes about 10db to double the perceived volume level. You won't notice much going from 18 to 30 watts. You probably will notice going to 60-80 watts. At lot depends on the amp design-some have a lot more headroom than others. Consider something like a Pass Labs, Threshold or Aragon that are class A rated. Some of them will be very warm for the first 10-20 watts but will have lots of power available after that for peaks.
Of the group you mentioned, I'd be leaning towards either the BAT or the Music Reference.
Personally, my experience with the McIntosh MC275MKV with upgraded tubes was very, very favorable... and the amp has plenty of oomph and runs cool. The stock version can be had for around $2700... just add some Telefunken's and Gold Lion KT88's and your in business. Resale value is outstanding as well.
Acresverde, I understand your fondness for the M60's. Wonderful amps, but even Ralph from Atma-Sphere acknowledged that my room is too small for them in a previous thread here. An old friend of mine also owns them, and his room is significantly larger than mine, and we were too hot to be comfortable after a two hour listening session there last month, much less than in spring and summer.
If I may make a recommendation though, if you have not had yours upgraded to 3.1 I would strongly suggest that you do. The improvement in his after the upgrade was remarkable, and the pricing from Atma-Sphere is very reasonable, especially as you receive a brand new warranty following the upgrade.
Elevick, thank you for your thoughts. Based on all of the comments, at one time, I was actually remotely considering one of the old Threshold's, but was worried about them being 20-25 years old, and what updating them and performing maintenance would cost. Also, several threads here indicated that they have been significantly surpassed in sonic quality by the newer Pass amplifiers.
Of those, the 30.5 would be all that I could likely afford, and I don't think they would have the power I need.
I had three versions of the predecessor of the 17.5 and would certainly concur that those speakers sounded best with at least 35wpc. Every time I'd try with less (several attempts) they were quite limited in what they could do. That said, sorry, I have no direct experience with any of the amps you are considering. I really liked Quicksilver amps with the Silverline speakers. Mini-mites actually sounded great with them. I also thought the Mesa Baron was a kick in the pants with those speakers. Actually I can't think of many bad pairings other than those where power was lacking. The most surprising of those was an Aleph 5 which should have been plenty of juice but just sounded flat and underpowered, lacking in dynamics with those speakers. sorry I can't shed more light on your specific considerations.
Check out Quicksilver,you can roll many types of tubes with them.
I would buy one of the used but modified Counterpoint SA-220 power amps being sold here on Audiogon and if you are handy I would then add additional modifications recommended on the Alta Vista Website. In comparision to many other amps my modified Counterpoint is one of the best amps I have ever heard within its price range and can drive any speaker. It will cleary beat any of the amps recommended above in my expereinece and in direct comparison.
Let me throw a change-up here. You can get a used pair of Manley Snapper monoblocks with 100 watts/channel of beautiful EL-34 output for well under your budget amount. You'll have more than enough power in your small room with your speakers and you'll get exquisite sound from these amps. I've owned lots of different tube amps (including SET) and the Snappers are my first EL-34 amp. They're keepers in my book.
Of the speakers on your list, I have only heard a Moscode 401HR paired with Silverline speakers (Sonata III). This was not an ideal match IMO.
What I would recommend without hesitation in your 10x10 room is a used Pass Labs XA-30.5. It's within your budget. Alan Yun uses Pass Labs amplification at audio shows.
The only downside is the heat produced by the amp in your room. It will get warm. Listen nude. It'll be worth it.
For a hybrid, the Van Alstine Ultra 550 is worth a look. Very fast, great imaging.
Here's another option I'm sure that you have already considered: lose the amp altogether and substitute Meridian DS speakers for your Silverlines.
It's a different sound to be sure, but I find the DS5xxx speakers are very neutral and can be tuned to the room somewhat via the integrated DSP. Just a thought...