I think the main problem I have found is the lack of a high pass filter the front speakers are trying to play for too low. Have now fitted a small 2x30rms amp to run standard speakers just to use the hpf on the amp has made a big difference. Set it to about 70 and am waiting for my alpine swe-815 to turn up. Will more then likely in future change front speakers.
When i wired it in I tagged it in to the rear speakers, it gives it a more surround sound, could be better but not by a lot I might upgrade the standard speakers later on but happy with it for now