Previously I discussed the varios active crossover options. But which one is right for you?
MiniDSP is easily the cheapest option where US $125 covers a simple 2 way stereo configuration. DCX is the next step up and as this unit often can be purchased second hand, it can be very affordable. Thuneau Allocator will typically cost most, although this is highly variable depending on sound card choices, so you have some control there. DEQX is the most expensive option.
How many channels?
MiniDSP allows 2 inputs and 4 outputs, but multiple cards can be used to cater for surround systems of more complex designs. One master volume pot can control a number of boards. Given the low cost, MiniDSP boards can also be used to extend the number of channels for any of the other options. DCX has 3 inputs and 6 outputs and that will cater to most projects. 1 x 6 way, 2 x 3 way, 3 x 2 way are covered. Allocator both allow 4 channel, although if multiple sound cards are used it's possible to obtain more channels in running multiple instances of Allocator Lite. DEQX provides 8 channels.
Only DEQX and Thuneau provide phase correction.
DCX has a number of dynamic options that are not supported in the other options. Dynamic EQ allows the EQ settings to change with level. This means you can compensate for the insensitivity of the ears to bass at lower levels, a very handy feature. It also has limiters so you can make the system "teenager proof." You can also effectively dynamic driver protection so that bass is limited at higher output - effectively a rumble filter that only comes on at a certain level.
Ability to make quick changes
DCX wins here. It's quick and easy to tweak settings. Suppose you wanted to adjust the bass level as a particular CD or movie was bass heavy or bass shy. It's quick and easy with DCX. MiniDSP requires a PC to make any changes. I can't comment on DEQX or Thuneau.
DCX is a bit like a circus and it will annoy some. DEQX looks more hifi and with the other options you are in control.
MiniDSP is a new option and I haven't tried it yet. I'm not making any assumptions here as price isn't always a good indicator of sound quality.
The sound quality of DCX is a matter for debate. It certainly won't be more transparent than DEQX, but will you actually notice a difference? There is no shortage of people who claim DCX damaged the sound quality of their system, but that could easily be explained as bias against a pro crossover which many assume to be "mid fi at best." I suggest that those who have concerns make up their own mind, ideally with some sort of blind comparison. There mere suggestion of poor sound quality is enough to sway many away from a potentially great value crossover. Don't be too easily put off. Allocator will be as good as the sound card you choose.
Balanced or unbalanced?
In most home audio systems it would be best to run unbalanced lines. Where noise rejection isn't required, balancing actually adds noise. This is acceptable in a pro application where noise pickup over 200m of cabling would be a disaster, but for home use it's rarely a requirement. In the rare situations where long runs are needed, DCX is handy. You might put a concealed audio rack some distance away where it's convenient. Otherwise, this is a black mark for DCX.
Do you want a PC in your sound system?
If so then Allocator is probably your choice. This is a good time to consider other benefits of having a PC in your sound system as a media server for audio and video playback and storage. You can save some money here and gain a lot of new features, but it all comes down to whether you like the idea of a PC in the sound system. Personal preference comes into play.