I agree with N.A. if you want it to really "kick" you'll need more power than what the Sony is going to give you considering that the wattage will be split at the sub to feed the front speakers. Not sure of the % split but will be less than 100 watts.

If you can, try both amps at a dealer with a boxed passive sub approx. of the same size and quality to determine which one will "kick" more. My advice would be to buy a used amp of better quality and power to fit the budget (not sure if you are able to buy an used powered sub to steal the plate amp out of and retro fit it into another enclosure). The problem with a in-wall sub is that it may not be placed for the most or best bass.

Having said that you may be happy with the level that the Sony can provide and you being happy with it is all that matters