Is my new amp TOO GOOD?

@mulveling In the 200's I actually preferred the KT 170's over the 150's.  To me the KT88's sounded a bit anemic. The current sound is actually quite well balanced but there is a little too much sizzle on the upper end.  Some snare drums explode out of the speakers.  In truth, my ears have always been sensitive to upper frequencies though.  Also the dynamics are much more pronounced with the 300's, which is taking a little bit of getting used to.  I don't quite have 100 hours  on the tubes.  I did talk to Kevin and have changed the stock 6SN7's to my NOS RCA 5692's which has also helped somewhat.  I do like the idea of changing to KT120's but I don't have them anymore-they went with the 200's on the trade in.  I still have eight each of the KT 150's and 170's.  I guess I could change a row in each amp to see how that does. I would check with Kevin first. My speakers are early Magico S7's (89dB).  Appreciate your input.

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@mulveling I talked with Brent who confirmed that rolling should be done row by row.  Actually he said I could mix and match with no ill effects.  I switched the first row out with KT 150's.  Surprisingly little change.  Then I switched the back row out with 170's (my preferred tube in the VAC 200) and that took the majority of the shrill sound out, but it seemed overall a little "muddy".  I switched the first row back to the KT 88's and this seems to be the best compromise.  I've learned some things in this current upgrade.  Alll prior upgrades did nothing but add good to the system.  I could turn up the volume with impunity on almost all recordings. Everything sounded better. I believe this current upgrade shows the "truth" in the recordings and some recordings are just best not cranked.  The detail and staging is incredible  now and well worth the time and energy to sort it out.  I'm adding a Shunyata T30 Typhon and hoping that will also add further improvements.

Before you spend more money, try facing your speakers straight ahead (no toe-in) and placing your listening seat closer to the plane of the speakers compared to the distance between the speakers. That should reduce the treble energy you're hearing and may take care of your concerns. It will also enlarge the size of the soundstage, as a bonus!

@mojo771 Can you give us an update, did some break-in time resolve your issues?

@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.