I don't know what the result will be. It does sound like your pre might have some issues. Suppose the tech fixes the PSU or other issues and you get it back. Now quiet, functioning properly etc what if it has no identifiable sound quality? I think SIY's point that it probably doesn't have a sound if functioning properly is not so extreme.
Here are measurements done by Stereophile for a Modulus 3A.
Sidebar 3: Measurements Line-level measurements of the Audible Illusions were taken from the CD inputs to the main outputs; the phono measurements were taken at the tape outputs. The Modulus 3's output impedance at its line output measured 1775 ohms (L) and 1802 ohms (R) with the level controls...
www.stereophile.com
There not a lot there to make you think it has much of a sound. They do note moderate levels of DC output and that they fluctuate considerably. Maybe why you have gotten the pops on your amps at times when turning them off. They also show a rather high output impedance which might dull the sound a bit with some cables.
Tubes, Tubes, TUBES! They have great musical sound.......or so goes the myth. Just put tubes in the signal path and you might like it. You probably will like it better. I used tubes for years, and years. Tube power amps have a sound. Tube pre amps, not so much. SS pre amps not so much. So many want that tube sound and think a tube preamp gets that without the hassle of a tube power amp. Sorry, it very rarely is so.
Now if you just like the idea nothing wrong with that. But you seem to be suffering lots of trouble to gain something that is based upon a myth. SIY is actually trying to help you out.