SUTs have come a long way recently. Reducing the inductance has made them more transparent. An active stage has to do a lot to the signal and you are actually introducing a lot to the signal path with an active stage. You are introducing another stage of amplification (at best FETs) along with connnecting cables inside the box or outside the box. Most of the connections inside the box are on printed circuit boards, and not point to point wiring. A well designed and executed SUT will convert the current to voltage so the phono stage will think it is seeing a MM cartridge instead of a MC cartridge. Yes, we are dealing with extremely low signals, but you can't make a generalization that SUTs by design are inferior to active stages. I have heard many well designed and executed phono stages. The best active phono stage I had heard in my own personal system was in a KRELL KRC-HR, which I still own and use for comparison. Currently I am using a MM stage from a Liberty B2B with a SUT that outperforms the KRELL, which I am just using right now as a preamp and bypassing the phono stage. What matters to me is what sounds the best. I go to a lot of audio shows and listen to systems at peoples homes. When I substitute a SUT in their system and bypass the MC sections, most of the time, there is a marked improvement in sound. Sometimes not. It is system dependent. I cannot tell you that a SUT is better than an active stage in all cases, just like I can't say that an active stage is better than a SUT in all cases. You have to consider the cartridge and phono stage combo before making that determination.
