Is my new amp TOO GOOD?

@orthomead 
Glad you're found a better balance! You can probably refine more with the tube selections over time. The 300's are by far the most "chameleon" VAC amps I've had so far. They are VERY dynamic as you noted. Lots of bass impact, slam, wallop. They sound LARGE. Their sonic balance is also wildly different in mono vs. stereo mode, and very also different with different KT power tube types.That's very interesting you can mix rows! I hadn't thought of that, neat.

However yes the stock voicing in stereo mode (Russian KT88 and 6SN7) was too aggressive / forward for me. I've kept the stock Tung-Sol 6SN7GTB in those V2 slots because they're driving the KT tubes, and I feel that these stronger modern tubes retain more dynamics in this slot. But using sweet-sounding vintage tubes in V1 slots is a very good choice. I'm more a fan of Tung-Sol round plates (black glass), 1940's Sylvania, or Hytrons. I never got on that well with 5692's (in the past, different amps), and their voltage & power rating is much lower than 6SN7GT tubes, which in turn is much lower than the GTA/GTB tubes that the 300 has been designated to use - this could wear them out fast in V2 slots. Might ask Kevin about that to be sure.

If you do not like the sound, how can it be too good? 

Too new, not too good.  Let it burn in for 200 to 400 hrs, then tune with cable adjustments and speaker positioning if needed.  

@mojo771 

What you’re describing is obviously not post/pre-ringing from the tweeters.

So now I have much more detail, but its sometimes too much.  Higher frequencies - like high pitched loud vocals, and some of the detail now sounds almost like static.

if the above is true, AND If another track sounds "warm" in comparison, then you’ve built yourself a very resolving, time domain accurate audio system.

The high pitched vocals and what sounds like static are in fact microphone hash/glare, and sometimes even noise from the recording console. It's not really "worse" You are just "hearing more of the recording." 

If this is true, you’re basically at my level and that took me over 25 years! 

I think your system truly resolving from what  you wrote - regarding how it sounds.

What speaker cables are you using? 
 

If you are using cables that are lower tier from a higher end brand I have found a lot of them to be tipped up. Analysis Plus and especially Nordost were pretty bad. 
 

My new Snake River Audio Signatures seem incapable of sounding shrill. They are real good in my system. Not the case with the Straightwire cables I took out. Like night and day difference. Mid bass texture and tone went up several notches and any glassiness on the top end is now non existent. 

@gjfalls 

Nice system, mine is almost exactly the same, except I am running an older C2300 preamp into a pair of mc275s monoblocked.  I am using very detailed speakers and I feel the combo works extremely well.  

@mojo771 

You have already received great advice...  Toe out, and Break-in.  As you already found, I can validate that in my system, Toe out, and height of the speaker, made differences in high frequency perception and sound stage.  
Another tip I found in the McIntosh forums was vintage Telefunken smooth plates in the preamp line stage and phono stage.  I tried them, liked them, and kept them installed.  They can help smooth and sweeten the top end, but, it will not be as noticable as "Toe out" differences.