Okay looked closer at the spec/manual, it seems the Aiwa amp in that set provides separate amplification for the mid-hi vs lows for that Aiwa speaker, the amp spec:
Amplifier section
Mid-high frequency amplifier:
8 W + 8 W (200 Hz – 20 kHz,
T.H.D. less than 1%, 16 ohms)
10 W + 10 W (1 kHz, T.H.D. less
than 10%, 16 ohms)
Total harmonic distortion 0.15 % (5 W, 1 kHz, 16 ohms, DIN Audio)
Low frequency amplifier:
25 W + 25 W (35 Hz – 200 Hz,
T.H.D. less than 1%, 6 ohms)
30 W + 30 W (75 Hz, T.H.D. less
than 10%, 6 ohms)
Total harmonic distortion 0.15 % (12.5 W, 75 Hz, 6 ohms, DIN Audio)
So seems that it's pretty specialized for the matching Aiwa speakers and may not work so well on the Polk. Maybe putting your amp board to use would be better. Have you experimented with both sets of speakers with it?
nd could be of limited use on the