I have auditioned about a dozen SUT's for my Koetsu's (originally had Redwood Platinum and now have Onyx Platinum). My two favorites are:
1) Choir Audio H7. It uses the best available transformer from Hashimoto. Price is $1679 and Choir offers a 30 day in home trial.
2) Cinemag 1131 (blue label) from Bob's Devices. Price is $1195
I have purchased both. In my system the Cinemag has better overall frequency extention while the Hashimoto brings out the famous Koetsu midrange a bit better. Both have a very large soundstage and I recommend both highly.
1) Choir Audio H7. It uses the best available transformer from Hashimoto. Price is $1679 and Choir offers a 30 day in home trial.
2) Cinemag 1131 (blue label) from Bob's Devices. Price is $1195
I have purchased both. In my system the Cinemag has better overall frequency extention while the Hashimoto brings out the famous Koetsu midrange a bit better. Both have a very large soundstage and I recommend both highly.