Uh, the mp3 data is fed to the decoder chip in the MAS player device via the parallel port; Paula works independently and feeds her output through the MAS player to the same amplifier that the MAS sends to. The Paula output is Passed-Thru the player so one needs only one amplifier/speaker input. One could have both outputs playing at the same time, but I don't know what the point would be. It is possible to have Paula feed into a sound card like a SB128, then feed the sound card thru the MAS player to the amplifier/speakers so that all possible sound output goes through one input.
The MAS player does its job with all of my mp3's and a minimal work load from the CPU but it does stick out 4 to 5 cm in the back, and the device does not amplify the signal so the output must be amplified before any real volume is noted. I enjoyed mine a great deal.