is a subwoofer for music a good idea??

Yes it is a good idea. One suggestion is REL...

In my experience, adding a sub can really help, but only if it's a good sub and only if you really work at positioning and room treatment...or if you 'cheat' by using a parametric equalizer.

If you're willing to go up to something like the Rel Strata and spend the time needed to set up your system carefully, you might benefit a lot.

Get the best used sub you can for that price. Try it for a couple of months. If you don't like the level of quality it provides sell it and keep saving your money for a better one. But the answer to the question of whether or not to get one is a slam dunk... yes!

It's not just about reproducing the specific low fequency instrumental sounds. It's also about energizing the room. A good sub, especially if you are using monitor speakers, will allow your music to float in the air, it will make the whole experience more musical.

Look for one you can adjust for frequency response, phase, and "slam." Then plan to spend hours adjusting the location and other parameters to optimize the sound for your unique room and personal listening tastes. When you get it right, you'll know it was worth the trouble.

I have been particularly pleased with my REL subs.

Subs and mains should not overlap. They should be set up to merge at a point where they are both 3 to 6 db down. Combining the output of the two sums them together and produces flat response. Overlap creates a big hump and sounds muddy and bloated. Keep subs crossed very low and just loud enough to contribute impact and weight as needed. Adjust phase according to placement.