Parasound A21+ vs MF M8 500S vs Cary 200.2 ES vs Hegel H20

Your observations on  Silverline Sonata III's are a bit odd to me: I also own these speakers (though I listen to a different pair now) and I've paied with with a Cary SLI-80 integrated (85wpc in the UL mode, as claimed by the manufacturer), a 12wpc Chinese SE amplifier powered with EL-34 tubes, a vintage Sansui AU-517 integrated amp (65wpc), as well as restored vintage Eico HF-81 and ST-40 integrated amps, and each of them sounds great with Sonatas. My listening room is small (I don't remember its exact size),so the power is enough for it even if I listen late at night at low volumes. Does changing speaker placement, cables and other tweaks help? 

Thanks guys,

My room is larger at about 19x22x8 and the corner behind the listener's right shoulder is open to a long hallway and an open staircase. Speakers are 9' apart and I sit 12' from each speaker. Speakers are toed in half way between straight-ahead and at-the-listener and over the years I've found this to be the best setup. Baffles are approx 4' from the wall behind and the wall is 4' behind my head. Room is acoustically treated and nicely balanced. I don't listen to metal or at ear bleed levels but like to listen at a volume that gives the impression of a live performance.

I should emphasize that I'm not looking for a paradigm shift in the sound, we are talking fine tuning here. The current setup sounds great and 3D and organic etc but the higher powered solid state integrated amps I mentioned brought the system "alive" with more zest and vigour. The current system sounds slightly polite in comparison.

I'm just seeking a little more zest, sparkle, punch and slam. Imaging is already fine but I feel like I'm "seeing" the live performers in the room in front of me (i.e. from speakers back) but I'm not quite feeling immersed in the live performance. Sorry, I'm not sure how to explain this better.

I'm not sure if it was the higher current provided by those higher powered SS amps that "woke the system up" or a more extended top end or both. It is almost like the system is too polished and needs a little edge or crisper leading edges.

Tvad - You may be right about the Pass amps as they may provide higher current than my Rogue and perhaps greater transparency. But, I don't want a physically big, industrial looking and hot amp (it is not a dedicated music room or man cave). Many years ago I had a Plinius SA100 mk3 amp, but not with these speakers. It would have been interesting to hear it with these speakers although it too was big, hot and ugly.

Unison77 - you have obviously used a range of tube amps with these speakers and apparently not suffered the "politeness" issue that I'm trying to address. This makes me wonder whether I should try to borrow another pre-amp to discount it as being the culprit (although I recently re-tubed it) as I've used it for about 10 years now.

I know the speakers are fine as they came alive with zing and punch with the higher powered SS amps. 

I appreciate your input, please keep it coming.

Just a quick thought because it sounds like you did like the Kinki.

My wife and I just got a Kinki EX-P7 & EX-M7 into our Focal Sopra 2s.

It sounds open, alive, and true.  Maybe revealing would be a good word too.  I am not sure what dry means.  (We tried a Pass XA-25 thinking it would be the choice and it sounded like someone had put pillows in front of the speakers. I wanted to love it but it drove me nuts.)

So, maybe consider Kinki separates.  I read in research and it seems odd, but something we might try in the future, that many people actually prefer a Denafrips preamp to a Kinki preamp with the EX-M7. 

Though our next step is to try a Decware amp! (in a year or so.)

Anyway, have fun with your search & keep auditioning at home!

oh boy, where to begin...
first off i have had the stereo 100, the cary 200.2 and now have the parasound a21+.  
the stereo 100 was an awesome performer and very dynamic, the a21+ sounds hesitant by comparison - but - you have to use the balanced connections on the stereo 100, ultralinear mode and 8 ohm tap.  anthying different will shoot dynamics in the foot.  
i used the rogue audio RH 5 tube headphone amp linestage (stereophile class A, 2500 retail) which is a balanced design.  what a driving dynamic sound, the most powerful 100 watt amp i have ever heard, tube or solid state, used with connections and settings as mentioned.  sounds just popped and i wish i did not sell it.  
try the high gain on your herron if you havent, maybe that will help.  
the cary 200.2 sounded more dynamic, actually too dynamic whether balanced or slightly tamed down using rca connections.  it was super midrange forward though, almost shouty.  i had to part with it.  
the a21+ has excellent tone and transparency but not the best dynamics. 
to get satisfactory dynamics i bought the cary slp 05 preamp and that did the trick.  the cary is an amazing sounding preamp, also balanced connections.  
try bumping the herron to high gain, possibly more dynamic tubes?
run the st100 ultralinear, 8 ohm taps.  report back.  
based on my experience a different preamp will definitely do the job with the st100
good luck.