Koetsu work very well with SUTs into an MM stage, but that PH7 phono is not at all flexible enough to use like that. I say it’s absolutely to get a new phono stage. Don’t invest so much into such a wonderful cartridge and then squander it!
I gotta agree here. The gain is 57.5dB for both moving-magnet and moving-coil cartridges and the output from either goes through the same inputs and circuitry so you can't avoid the first JFET gain stage before going through the next tube stage (4 x 6992's). The PH7 handles all carts the same. Even if you could bypass the FET-based initial gain stage I'm not sure I'd want to try to use a SUT through four 6922's using a 0.2mV cart - likely would be too noisy. It seems this cart is better suited to SS phono pre. Just my opinion.