The differences are minor. The Tribute is more neutral, the Monolith more tubey (tiny bit). Craig and I rated the interstages from 1-10 with 1 being the best and 10 the worst in terms of clarity and "transparency". The scores were 1 for Tribute, 2.5 for Monolith, 4-5 for the original Levi Tango, 5-6 for the Hammonds (I am expanding the differences much more than they really are). The idea for the Monolith was for the Asian market (slightly different tastes) and also because we were not sure how quickly Tribute could crank out their interstages. The Tributes have a nano-crystalline core. The Monoliths and Tangos use an amorphous core. If I don't know if there is a "sound" to the cores, or maybe its because there is some similarity with their constructions, but the Monoliths and Tangos have a more similar sound which can be described as more "mellow" and "wet". The Tributes are amazing in that I have not heard clearer, "more resolving", highly quality bass from any other tube amp. We are talking about bass quality texture, slam, etc. which betters any SS amp I have heard (keep in mind that I am biased here.) As for the Monoliths, they are only a tiny bit behind in bass quality, but they bring a little bit more of that "tube" sound out. Now keeping in mind a discussion that this forum had in another thread regarding "there is always something better": the Monoliths are much more transparent than the Tangos (which was the previous benchmark). The Tangos sound murky in the bass by comparison. I mention this because I know some people here have heard the Levi/Tango amp. The real impetus was speaking with Ravi when we had the ZD Super and Studio T lined up next to each other. Ravi was blown away by the Studio, but remarked that he liked certain things about the ZD Super. The way the Monolith equipped Studio M sounds can be described as like the Studio, but with a touch of the ZD, with a small cost in technicalities. Ravi was like "I don't care, I'll take the M. What are you getting?" I told Ravi that I was getting the M. For the record, I think Craig might prefer the Tribute by a bit. So even between Craig and I, there is some minor disagreement on which is "better". We both do acknowledge the nature of their differences, but we also feel that the differences are so minor. Both the Monolith and Tribute are by far the best interstage transformers we have heard to date. In the end, there is a reason why the Studio (with the Tributes) is called the Studio. Anyone expecting a tubey sound amp with the Studio T, will be disappointed (I think you guys already know this); and the Studio M won't that much more tubey either. So really, I think it comes down to a matter of taste. And also maybe availabiilty and timeliness. At this stage in the game, I'd take either one. The Studio M is expected to be more expensive than the Studio, but the price will be kept the same for anyone on the Studio T list that wishes to transition over. The initial run of the Studio M will be five units. We can sign people up on the Studio M list from the Studio T list without them losing their spot on the Studio T list.