I had the PSW-1200 as my first sub. Bought it in the mid 90s for about $350. 12" driver with 120Watt amp and a single 3" (IIRC) port in a small box (compared to some subs of today).
It was really good to begin with, but it was my first sub. I had little to compare it to. When I upgraded in 2006, I expected to pay $500 but wound up buying a sub that cost $1,400. I just couldn't find anything in the stores that were better than the PSW-1200 in the $500 range. To make this short, my new sub made the JBL seem such a weak performer that I never regretted replacing it or paying as much as I did to replace it. I gave it to my neighbor as I no longer had a use for it. If you can get a good sub, you will know what I speak of as the impact, clean volume, overall sound quality of better, but more expensive, subs will impress you.
As far as setting it up, on the JBL put the phase switch to 0, the gain to around the 10:00 position, and the crossover to max. Then follow the Denon instructions to complete the set up.