Hi AssFault, congrats on the CSP2+, it`s a great tool for delivering the signal to your amp. The pre in/out volume pots are really trimmers to suit your ears so you can dial in your front end before using the main volume. Subtle differences which are lost on me, and I sometimes use the pre in/outs as master volume settings if I want to keep the main volume knob in one position. No problem in using them which way you want.
The only time I`ve experienced the intermittent`crackling` is when the power cord is just making good contact, and this can happen on any of my Decware amps. Yes they can seem a bit loose, it`s more a safety feature. They`ll come out easy if accidently knocked of a rack etc. You have to get them `just right`which can take a little time. Once done they`re no prob.
Of course there maybe another issue and the obvoius culprits, tubes, tube seating, i/c connections are ones that come to mind.
Dont know about taking voltage readings.
Hope it`s a small issue and you get glitch free sound soon.
Syd.

I get the concern about the volume pots, though I have never heard my own crackle without movement, and then not the stepped pots. I think the calibration is a setup and test thing and as Syd suggests, the pots are about user adjustment.

A good start point for the silver in and out pots might be 9 (one notch back from full open) on the inputs, and 5-7 for the outputs (say 6...four back from full open.) Especially on the outputs, this will modify the CSP OTL effect and sound density. Lower/leaner, less CSP effect, and higher, more. If you don't hear crackling with changing these then I would start by finding starting place where you get the best sound and use the front pot for volume. Does it crackle when you move it? Mine does now, but I never hear it in the music so have been lazy cleaning it. It may be time to clean yours??? I find it is good to explore the silver pots a bit now and then for ultimate sound. And what sounds best may change a little as you get to know the sound or with different tubes.

Also, I wonder if you have spare tubes you can check. Since the noise is in both sides, it may be the input tube. Or just a weak tube connection can cause crackle. Cleaning the tube pins and socket is something I do when I hear weird noises that seem tube related.