If your subwoofer has high level (speaker) inputs, that's what you'll need to connect to your amp's speaker outputs.
That's an interesting old amp you've bought there.
Modern amps are all about signal purity - meaning they keep the signal path as short as possible, not least by using a minimum of switches.
Your PM-500 is sort of the opposite of that, they didn't care back then.
You've got 2 tape monitor switches on that thing. Those switches take priority.
What that means is that your 2 line sources on the selector switch (Tuner and Tape 3 / Aux) need to pass through a total of 3 switches on their way to the amp input.
Whereas tape 2 goes through 2 and tape 1 only goes through 1.
That all becomes more relevant if / when the switches become contaminated by dust and dirt - resulting in crackle and signal loss.
Feel free to ignore me of course but I would advise connecting your most important / most used line sources in the following order with 1 being the most important:
1 to tape 1 play input - using tape monitor 1 to select it.
2 to tape 2 play input - using tape monitor 2 to select it.
Least important inputs 3 & 4 to Tuner and Tape 3 / Aux inputs selected by the source switch - with both tape monitor buttons off (out).....and leave the tape copy selector set to off.
For maximum quality you would bypass the equalizer too - but I can understand that you might want to be able to use that.
Nice looking old thing - enjoy it
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