I'm using a PC's 3.5mm jacks to send a signal to a cheap stereo amp, which then powers my front speakers. I'm also using the subwoofer out on the PC's 3.5mm jack and converting it to RCA, which then gets fed to the self powered subwoofer. The PC controls the crossover settings. The problem is...

On denon receivers if you set your front LR speakers to large and enable the double bass setting you can still set the crossover from the LR speakers that you want your sub to play also. So although the LR speakers will play the full band signal you get to select how much of that signal you want...