All stereo amps support subwoofers. You'll either use the high level outputs, or the low level outputs.
Then adjust crossover on the subwoofer itself.
Some may have a subwoofer out but this is a downmixed L/R to single RCA, which works fine. It'll be full range.
So just make sure the subwoofer you buy has the right type of input to match the output of the amp.
If you want two sets of speaker outputs, I'd make sure you find one with switchable A & B, so you won't be overdriving the amplifier.
Quick search shows
YAMAHA
RS202D
That has no line out for sub, so you'll just pair the L/R speaker outputs, it won't use any power from the amp. So you need a subwoofer with high level inputs.
Try to get a subwoofer with high pass, on the high level inputs. That way you go from Yamaha 202D amp, speaker level output into the subwoofer high level input. High level output from subwoofer into speakers.
Because of a high pass, the speakers receive only 80hz and up, and the subwoofer only plays 80hz and lower, so speakers are not trying to reproduce frequencies they cannot handle. I do something similar myself but on a pre-power, with a high pass crossover between the pre and power amplifiers. But it's the same principle.
edit if you use the line level outputs from the amp to a sub (or indeed a power amplifier) You'll need a amplifier with pre-outs at least L & R, or if the amp has it, subwoofer pre-out.
Pre-outs are volume controlled. The standard line level outputs are fixed at 100% so will be unsuitable for subwoofers, or power amplifiers.
