Bob Carver "Black Beauty 305" or the E.A.R. 890

Yeah, I'm with you there. I'd have to hear the SS amp first, and I'd be very wary of amps with a reputation of being analytical or bright (a reputation that seems to follow the Bryson amps to some degree). I owned some Parasound JC1 monos a while ago that had a very nice sonic balance for SS, and with plenty of power on tap into 4 ohms.

I didn't put it in the title because it is a second discussion... but, audio guy I'm working with suggestion was a choice between the Carver and the Bryston 28BSST2 (at 1000 wpc). I have a tube pre-amp so there would still be tubes in the system. I love the sound of tube amps -- if I go that root for more power I'll have to listen for a while before I choose.

Also, your 24' x 27' room would be considered quite large! Indeed, I would suggest you require quite a healthy dose of power unless you *always* listen at very low volume levels. Really, your power needs are dictated more by the peak/crest levels you hit rather than your average levels -- these peaks can shoot up surprisingly high on high dynamic range material (classical), but they're typically very close to the average level on highly compressed rock/pop recordings.

+3dB is (almost exactly) twice the acoustic energy -- that's not subjective. How much "louder" it sounds to a person is somewhat subjective. Some folks prescribe that +10dB constitutes a doubling in perceived volume, others say +6dB; personally I find even +3dB to be quite significant, and +10dB sounds a lot more than just twice as loud.

With the Magico S5 you're REALLY going to want more power than 70 Watts. They're nice speakers and I've heard them do OK with 180 Watt/ch tube amp on the 4 ohm taps, but when mistakenly moved to the 8 ohm tap (reducing power and increasing distortion, i.e. sort-of simulating a lower powered tube amp), the result was awful.

The Carver 305 should have enough power to do just fine. However, the S5's 89dB rating can be deceiving in that it's a sensitivity spec and these are 4 ohm speakers; tube amps will only yield 86dB/Watt here. A high-end SS amps will typically "double" (not really, but close) its power into 4 ohms; thus, the nature of this speaker works with SS and against tubes. I'm sure they were designed with high-power SS in mind. Also from what I heard, they'd probably benefit from higher damping factors as well -- again, lending themselves to high-power SS.

In summary, with S5 I think you'd have a bad match with the EAR and a potentially good-to-great match with the Carver, but other (SS) options may be even better. I'm a tubes guy, so it takes a LOT for me to consider SS options over tubes, but I think the S5 may be one of those special cases.

Right now I'm powering a pair of B&W 802D's but I have a pair of Magico S5's on order. The S5's are rated 89dB where the 802's are 90dB.

How big is "big?" The room is about 24' x 27'

I don't have a problem filling the room with a single E.A.R. today (70wpc). When I think about the formula that doubling the power brings "just" 3dB more... given that dB is a log scale doesn't than mean 30% louder?

I don't listen to much music at high volume - so, the question is as much about the "quality/qualities" of the sound.

My only thought was how loud do you want to play your music? Then I remembered that some people have big rooms to fill. Even then when I lived in a relatively large home with a big formal living room, I was able to get all the volume I needed from 40 to 60 wpc, using 88DB sensitive Von Schweickert VR2s. What are you aiming for?
I will hazard a guess here and say that either approach will work, I am rooting for Bob Carver's comeback but recognize the quality of the longer standing E.A.R. amps.
I used to keep a variety of amps perhaps you can keep both.

Like the answer to any nontrivial technical question, it depends. Even just +3dB of extra headroom can yield a huge difference -- but it all depends on your listening habits (typical & peak SPL), speakers, seating, and room. If you shy away from loud volumes or have extremely efficient speakers then the +6dB itself likely won't matter, but you'd still hear a sonic difference between the 2 amps. Then, there are other complex interactions between amp & speaker that aren't necessarily related to the power output -- and that's where it gets tricky, and matching becomes more of (or at least partially) an art.

Nobody here can provide better than a wild guess about your power needs without the above details.