I've owned a few preamps, the JMP-1 , VHT GP3, I still have the Mesa Triaxis, and now the M4.
My opinions on them are: ( subjective, of course)
VHT-Gp3 - Nice idea, but falls short concerning gain. Limited midi capability. A pain to change tubes. Midi dip switches in rear, you change channels easily.
JMP-1- Versatile, nice cleans, but all gains sound of course Marshall, that 's what they intended. FX loop- weird rise in volume below settings of 5 , stereo outputs. Midi capable with all EQ settings saved in presets. Again- major pain to change the 2 tubes.
Triaxis- If you like the Mesa sound, and only Mesa, this is the best pre-amp with stereo record out, direct stero out, FX send , return stereo. 8 different Mesa type modes. Fully midi capable. Downside- all low/high gains have the Boogie sizzle highs. But overall functionality is great , except the seemingly useless fx level control. All 5 tubes are open to the rear and easily changed .
M4 - So far I prefer the sound over all previous preamps. The module selection is endless, and if you're like me and your musical interest is more eclectic, there's a module to suit it. The down side is a lack of features, but in the interest of avoiding digital processing, there must be a trade off. It would be great to have stereo output, stereo FX returns, full settings save and recall, but I can work around it. How many presets do we really USE anyway ?
Tubes are easily changed in the rear of the enclosure. AND why do they hide the midi-dip switches inside so you have to remove a few dozen screws to change the channel ?
How about an access door, maybe slide it open, change channel , slide it closed.
I have not tried the Prophesy, but if it's anything like the VooDu Valve there's one tiny little 12AX7 tube hidden deep inside , wrapped in foam (yes), just so they can call it a Tube Preamp......
H