I have a few Koetsu Platinums, and I know for sure I prefer them with higher ratios/gains to bring out the dynamics - 30x SUT or an active stage with 69dB or more seems to be ideal. I know this is higher than the usual recommendations. I wouldn't even bother trying an 8x SUT.
I’m actually currently using the HM-7 with my Blue Lace and love it, but I kind of get what you say about its "larger than life" presentation. I prefer it slightly to my EAR MC-3 (I use it on the 30x / 4 ohm tap), but I really like that SUT too. You might end up preferring the EAR, but it’s not much more laid back in the treble if you’re looking for that. The Koetsu SUT might be more your style as it’s more laid back overall, but they’re hard to find, and currently I do prefer the more dynamic presentation of the HM-7 and EAR.
I’m actually currently using the HM-7 with my Blue Lace and love it, but I kind of get what you say about its "larger than life" presentation. I prefer it slightly to my EAR MC-3 (I use it on the 30x / 4 ohm tap), but I really like that SUT too. You might end up preferring the EAR, but it’s not much more laid back in the treble if you’re looking for that. The Koetsu SUT might be more your style as it’s more laid back overall, but they’re hard to find, and currently I do prefer the more dynamic presentation of the HM-7 and EAR.