Biamp question

oldhvy is correct in the bi-amp method, but an active crossover like russ69 mentioned is the better way to do it. You can limit the bass going to the mid/high frequency amplifier, reducing power and intermodulation distortion. This will make both the low and mid/highs much cleaner. An active crossover will also give that much greater ability for you to match the levels of each band. So many crossover choices, from DBX223, TDM24CX-2, many Ashley’s up to the Marchand, Bryston and First-watt at the top, in my opinion. You also have the choice of digital, Behringer and so many other DSP’s. We are all here to help, good luck!

Thank you all! I believe I can manage the active crossover (possibly) but my chief concern is disabling the crossover in my speakers. 

You can bypass the crossover in the speakers or you can leave it the way it is. The danger of disconnecting the internal crossover and running just copper wire between the low end and mid/high frequency drivers is the risk of damage to the midrange driver (the 7" in your case), should a power amp or the active crossover fail. You cannot bypass the upper midrange and tweeter drivers because that would mean you will need to tri or quad amp. I'm tri-amping with 3 stereo amps and a 3-way crossover, I also have 3 subs. The sound improvement with running just copper wire between the drivers and amplifier outputs, for me, is worth the risk of damage to any or all drivers. I recently lucked out during a very rare, (first time in 43 years) when the active crossover in one channel failed sending 500 watts into one woofer and 300 watts into one midrange for about 5 seconds. The tone was relatively high, about 900Hz., but any longer the drivers would have been damaged. Luckly, the tone was below the crossover frequency of the tweeter, so a clipped 200-watts rms signal was not seen by the tweeter! My suggestion is to take small steps. Leave the crossover in the speakers as is and as you get more educated and confident, you can try bypassing the internal passive crossovers one at a time. Enjoy!

I'd be careful with and active crossover that doesn't fail safe. A Behringer DCX2496 will fail to work but not send the wrong signal to the wrong place. I only use an active XO in my Bass management system. I find there is a lot better protection with a passive XO for mids and high. 300 hz and below I'm direct coupled too. No passive crossover. I don't recommend it, out of the gate though.. Hook up your amps and be happy. Quit making it complicated.. You want to mess around later, you always can.

Regards

If the output of the Parasound is louder than the Rouge then you are good. But if the Rouge plays louder, turning the Parasound down won’t work.

I’ve bi-amped with two of the SAME amp, but slightly different minor versions, and felt even that sounded a bit disjointed. So I’d be surprised if a high power SS amp and a high power tube amp meshed well. That said, the Rogue tube amp sounds much more akin to SS amps than you might expect for tubes. And the A21’s gain control is certainly an asset for gain matching the two amps. IF you find the Rogue’s gain to be higher than the A21+ at its max level, you can drop the Rogue down a few dB’s by subbing 12ay7 in the V1 / phase inverter slots in place of the 12ax7’s. It works well; I've tried this. I like the red-label GE 12ay7 from 1962 or 1964, I think (very specific year on the red labels) :)

A 5751 sub its also good for a dB or 2 and sounds nice on its own merits (if you have a good triple mica black plates vintage).