multiple Cab question
 

Lets say I wanted to add a second cab to my rig. I'd like to be able to dial in each cab independently; one for the lows/low mids and one for the high-mids and highs. Would i be able to run a DI from my current head into an EQ then into a separate power amp and be able to run and dial in the second cab?

You would be better off to get a preamp to crossover to stereo power amp. Use the attenuators on the stereo PA amp to do the final balance on the cabs.

I'd like to keep my current head to dial in the first cab, shouldn't i be able to use same head as a preamp to send to the crossover>poweramp>second cab?

Will it work? Yes.
Will it work well? Not really.
Will you have trouble with spill over from both rigs to deal with? Yes.
Will you be happy with the result? Maybe.
If you have a serial effects loop you can use the effects send to the crossover, highs to the effects return of your existing amp,that will help.

Been there done that. A big reason why a lot of bass players line out to the board. The only way to do it right in my opinion is to run two separate amps for each cab. You can even use a small combo amp or micro head to power a guitar cab for some sweet high that don't have the plastic sound of horn/tweeters but the issue is live its rare to get two channels of bass so the compromise is using the xlr out on a pre amp. Just because Stanley Clark gets to do it doesn't mean every joe blow bass player will get to. After a while you get used to it. All I see if blonde brunette redhead..... No seriously all matrix jokes aside I dial in my preamp in the studio or at home with nice flat sounding headphones and my power amp and cab is essentially a monitoring rig. For everyone that's tried singing onstage the floor monitors are rarely ideal but you get used to it and jam on.

I was planning on using two amps, my GBE1200 as the pre/power amp for one cab and a separate power amp to run the second. If i just run a separate preamp through the second power amp, which out on the GBE would be ideal to get an uncolored, unaffected signal to the separate preamp?