Self-made output filter on available module

I'm just moving from speaker building to amplifier building. I'm willing to build a my own Class-D amplifier. I confess that I don't have as much knowledge about electronics though. At the moment, the work I can do seems to be the output filter.

I'd like to ask everyone that are there any Class-D amplifier modules without output filter sold? If not, Is it worth if I would buy a complete module and modify only its output filter section?

My plan is to use a 4th order Linkwitz-Riley, or Butterworth if L-R is not possible, on the output filter. Is it an acceptable idea?

Will I also need to adjust the feedback circuit?
 
If your aim is to learn about the trade-offs involved in designing output filters then yes its a reasonable idea. If the amp module has pre-filter feedback then normally no need to change anything else when modifying the output filter.