Bi amp and bias issue


Hello I need help with biamping my magnepan 3.5r I have a krell Kav 2250 25.7 gain 2.53vrms input sensitivity for bass and rogue audio m150 29gain 1vrms input sensitivity.

I tried using stock crossover using krell for bass and rogue for mid and tweeter and it works but only when i use triode mode on rogue if i switch to ultra linear when I try to bias the meter on rogue oscillates. 
I contacted rogue they said its the tweeter load the amp is not designed to play just the tweeters but i tried running just the tweeter with it and not turn on the krell and it does not oscillate . 
I replaced the 12ax7 driver tubes on the rogue with 12au7 and that stopped the oscillation but rogue said they dont know how it will affect the amp in long term. 
Another problem im having is that the rogue plays alot louder than the krell

also if anyone is curious the rogues sound better playing the speakers than the krell rogues are 150 watts into 4ohm and krell are 500w the bass sounds better with most music including pop techno hip hop with the rogues the krell sounds better when theres alot of energy lots of fast bass sounds where the rogues dont have as much grip during those passages.

the rest of the system is denon dl103r mc /jensen mc transformer/rega p3 /hagerman trumpet phono/
128x128beep23
With two different amps you need an electronic crossover. That separates the bands and allows adjustment of the volume for each amp. Not sure about your bias meter oscillation issue. Maybe try the other speaker taps on the amp. The crossover might also help by stripping and separating the frequency bands, not sure but worth a try, otherwise you'll need a different amp.  
+1 for electronic crossover. This is an absolute necessity when you bi-amp. Also tube amps don't like low impedances, I would run in triode mode. I bet the mid and tweeter impedance is dropping below 4 ohms.
Thank you for suggestion of active crossover I’ve  been researching trying to find one that has single ended inputs because my preamp only has single ended out but cant find anything under 1k besides the marchand .
There are a TON of active single ended crossovers. Do you want rca or phone plugs? Balanced or unbalanced? Analog or digital? 2-way, 3-way, 4-way?
Rca analog please thank you I was trying to find one reasonably priced under 1k with goos sound quality.