Hey Hanneman213, did you ever get your wah/comp issues sorted ? IIRC that was back in 2015.
Just to confirm I understand correctly, it doesn't matter what patch voice etc you select, stage output B just has crunch like sounds, no proper signal ? What happens with the B cab sim out ?, does it work or make the same sound. Fx loop B send should also have decent signal (level will be affected by level buttons setting) but loop A and B sends should both sound similar (clean "signal" tone). So you can test those 2 outputs. I don't think this issue is tube related as the tube/gain stage is before the signal is split into A & B. Have a look in the front of the MP2 manual (page 4), the schematic there is reasonably easy to understand and you can see where the signal splits (after eq & noise gate). The signal splits into (pseudo) stereo at the chorus (whether it's on/in or off/out), basically the B signal is the A signal inverted. So the first place the B signal is available is at Fx loop B send jack (which should have signal regardless if the loop is on or off). But with chorus out/off, the B signal is still made by the chorus (the chorus circuit/chip inverts the A signal).
When the radio tune noise comes and then decreases, does it go away after a little time ? This is sounding like a capacitor dying, my guess, getting better as it warms up ??. But could be tube related.
The tubes probably need changing regardless and "may" fix the radio tune noise
. But changing them won't hurt anything and will make your MP2 sound better. The Marshall tubes are re-badged/branded, they don't make their own. I think they use Chinese tubes and paint their logo on them.
What county are you in ? can you buy tubes online from the US or Australia (or do you have import tax/restrictions) ? Also European tube prices seem to be higher than US and Australia from what I've seen. If you can buy tubes online, then I'd buy a pair of New Sensor 12AX7 Long Plate Mullard re-issues from Dougs Tubes. These are the tubes I use in all 4 of my MP2s because they work so well in MP2. Also if you buy them from Dougs, they test all their tubes thoroughly so the chances of a dud tube (and it does happen) are highly unlikely. (http://www.dougstubes.com/mullard-12ax7.html), there's even a review by me on there if you scroll down. And $20 USD per tube is about as good as it gets price wise.