An external active crossover system has a flow like this
source ---- active crossover--------amplifiers--------individual drivers
It's basically what you would find in sound reinforcement applications except in your case, shrunk down.
The thing is with internal actives where the active XOs and the individual amps are all in one enclosure with the drivers is they don't have the flexibility you've said you want. You could put an active cross over ahead of your active monitors and use it as a high pass filter and send the other part to the sub and basically leave the sub's setting wide open. Like you said though, you'll now be paying for more stuff that you won't use e.g. your sub's crossover and 2 bands of your active unless you can find a two-way active. Rarer but they exist.
DEQX isn't actually geared towards home theater. It is really geared towards applications like this. Room Correction is just a part of what it does. It is actually more prized as a cross over and especially for its driver correction capabilities. It is also a pretty transparent pre-amp which includes a remote. Not cheap though. It can be configured in practically any way you can use the 6 outputs. 3 Stereo Pairs, 6 Mono Signals, etc. Basically it does everyting you've put on your wish list. The Bheringer units do the same except the driver correction part and owners have noted that there is a bit left to be desired in terms of sound quality. Alan Langford of DEQX is a good guy. I've got his contact info somewhere on this computer of mine. I can look for it for you if you want.
If all you want to do is shelf some frequencies off the active monitors and the subs. Perhaps some parametric EQs would do the trick for you. Your chain would look like this
source(DAC) -------preamp outputs 1 and 2----------parametric for monitors (bass cut)-----------monitor
preamp outputs 3 and 4----------parametric for subs (Highs and Mids cut)----subs
More cost effective solution I think but again lacking that fine "tweakage"
source ---- active crossover--------amplifiers--------individual drivers
It's basically what you would find in sound reinforcement applications except in your case, shrunk down.
The thing is with internal actives where the active XOs and the individual amps are all in one enclosure with the drivers is they don't have the flexibility you've said you want. You could put an active cross over ahead of your active monitors and use it as a high pass filter and send the other part to the sub and basically leave the sub's setting wide open. Like you said though, you'll now be paying for more stuff that you won't use e.g. your sub's crossover and 2 bands of your active unless you can find a two-way active. Rarer but they exist.
DEQX isn't actually geared towards home theater. It is really geared towards applications like this. Room Correction is just a part of what it does. It is actually more prized as a cross over and especially for its driver correction capabilities. It is also a pretty transparent pre-amp which includes a remote. Not cheap though. It can be configured in practically any way you can use the 6 outputs. 3 Stereo Pairs, 6 Mono Signals, etc. Basically it does everyting you've put on your wish list. The Bheringer units do the same except the driver correction part and owners have noted that there is a bit left to be desired in terms of sound quality. Alan Langford of DEQX is a good guy. I've got his contact info somewhere on this computer of mine. I can look for it for you if you want.
If all you want to do is shelf some frequencies off the active monitors and the subs. Perhaps some parametric EQs would do the trick for you. Your chain would look like this
source(DAC) -------preamp outputs 1 and 2----------parametric for monitors (bass cut)-----------monitor
preamp outputs 3 and 4----------parametric for subs (Highs and Mids cut)----subs
More cost effective solution I think but again lacking that fine "tweakage"