preamp out instead of MC transformer

Not sure why you said "back into the preamp in." To have any chance of working, it seems to me that the output of the second preamp would have to go to the power amp.

Given that, while it is conceivable to me that the idea might work with certain components, in general there are all kinds of things that could go wrong. Depending on the specific designs significant concerns would be that dc offsets, turn-on transients, and/or turn-off transients produced by the first preamp could be amplified by the second preamp to potentially damaging levels. Low level hum that might arise due to ground loops involving the two preamps could also be amplified to very high levels.

If all of those problems could be avoided, it is probably more likely than not that the signal-to-noise ratio of the first preamp, with respect to its line-level inputs, and/or the gain of that preamp, would be too low, resulting in unacceptable hiss levels.

All in all, it might work under some circumstances with some components, but I don't think it is a promising path to pursue.

Regards,
-- Al

It is not even wrong, as Wolfgang Pauli use to say. A preamp output would hideously overload a MM input. I thought I had heard every strange idea in audio; I was mistaken. The good news is that this is a strong " worst idea of the year" candidate. I don't know enough electronics to fully describe why this would not work.

It is likely that Al is correct and the gain would be far too low. In my first response I had assumed that it might be possible; however , even if it were remember that the output of a line stage is measured in volts and the input sensitivity of a phono stage is measured in MVs so there is a probability that you will overload the phono stage. Considering the cost of extra cables and preamps a step up would be much cheaper and far easier to work with. Bob's Devices is a very good one at a moderate cost.