First foray into tube amps

I can understand why you are looking to use the DAC volume control and avoid a linestage or integrated amp.   On paper, most sources have sufficient gain so a linestage is not needed.  However, even if additional gain is not needed, most systems sound better with a line stage or an integrated amp.  Without this seemingly superfluous additions, systems tend to sound a bit polite and "blah."  The great thing about tubes is how lively the sound is compared to solid state at lower volume levels; that is best preserved with the added stages.

I suggest looking at amps that run the EL84 power tube.  These tubes work very well in lower cost amplifiers and should deliver enough power for your music preference and speakers.  I personally like the 6L6 tube and KT66 tube (similar to 6L6) but there are fewer amps made using those tubes.  I think this is the case because an amp built to run these tubes can probably be made to run higher powered tubes and power is something you can market more easily. But, to me these tubes are the ones to focus on for good sound quality.

@musicfan2349 

I suspect neither of us is saying the other is wrong, just two sides of the thing, yours a worthwhile contribution.

My comments are not absolute, but meant to be general considerations. I encourage trying tubes, and look to make it easier and successful, in most respects, less entry and future costs.

We need double the power to make a +3db noticeable increment of more volume. Then double again for a bit more volume, +3db in each perceptible step up.

That adds up very fast, and when you start at 83, up to 86, up to 89, you need to double your power twice. We start out needing only 1 to 5 wpc (which surprises a lot of people who do not have power meters). As you say, your speakers sound excellent but no way can you play them loud or too loud.

Your amp is 100 wpc, driving 83 db sensitivity.

My office, 10 wpc driving 90 db sensitivity

My main system 45 wpc driving 16 ohm horns well over 100 db sensitivity

OP speakers are 87 db sensitivity.

Like yours, my AR-2ax sound wonderful in my small office, however, I often turn the volume higher or far higher than I do in my other two systems, and it never gets loud or too loud. Thus, for very dynamic instantaneous peaks, it is doubtful in my mind that 10 wpc for 90 db sensitivity is ’enough’ or ’comfortably enough’, just as I might doubt that your 100 wpc is.

I mentioned keeping power needs lower, to get in a category of more competitive options, as well as the other advantages. 30 to 45 wpc is a very competitive group, 100 wpc less so.

I do not want to lift or move a 100 wpc tube amp. It’s heat is much greater, positioning restricted ....

The mcintosh  275 is 75 watts on stero.when you want more get a 2nd amp in the future 150 watts per channel in mono.that design has been around forever and just works.it will retain its value if you buy used version v1 or 6 is about 5k in your budget. Enjoy the hunt.

@elliottbnewcombjr Let's take another look at the OP's stated requirements and the room for them: "The room is 23x16x8 and is well treated.  I listen at low to moderate volumes, lots of vocals, blues, Argentine Tango, some classic rock."

As a former software engineer, I can tell you that requirements are everything...

Granted the terms "low to moderate" are somewhat subjective in nature, keeping in mind his self-powered subwoofers, I would think 75 to 100 WPC would be more than sufficient to drive the 8ohm Stirlings to pleasantly loud level without too much strain. 

Proceeding further here's a review of them:

Stirling Broadcast BBC LS3/6 loudspeaker | Stereophile.com

(Please note the wattages of the amplifiers used in the review.)

In closing, I would suggest that there are many reasonably priced tubed candidates for @treepmeyer to insert his system.

Happy listening.

@elliottbnewcombjr 

"We need double the power to make a +3db noticeable increment of more volume. Then double again for a bit more volume, +3db in each perceptible step up."

Elliot, you could also say that every 3 dB increase in a speaker's efficiency using hypothetically the same 20-watt amplifier is like doubling it's power output. Say, if you went from an 85 dB speaker to an 88 dB sensitive one it would give you a 3 dB increase in volume. Quite substantial from a headroom point of view.