I have two different models.
One works but it's auto-power (on signal detection) doesn't work - stays on all the time. I was able to open it up only enough to get to the amp circuit board, not not enough to non-destructively take apart.
I was not able to find a schematic but did look up the IC datasheets and typical circuitry. It had a 18 dB/octave low pass filter and IIRC an 18 dB/octave highpass filter as well. There were outputs to 'satellite' speakers (non-bass signal).
I plugged a guitar in and it was uncanny how below a certain note the output just disappeared.
The other amp also worked with the guitar (like part of the bottom string only), but I could not get very far into disassembling it.
Someday I'll try putting satellite speakers (little powered studio monitors) on one of them...
The short answer I guess is that the sub alone will probably only play bass.
I think they glue the krap out of them so they don't start to sound like one of those cars with the subwoofers and hardware rattling loose as they drive down the street...
Yeah the filter is my concern. I wasn't sure how complex the circuitry might be, if it would be possible to isolate or remove the filter. I pried around with a screwdriver but I don't think I will get it open without cutting it open.