If anything, it's just as important to learn what your personal monitors CAN'T reproduce as much as what they can and just how that translates into a mix that stands up to a vast array of playback systems. Proper room acoustic treatment and speaker placement really do go a long way in helping create an accurate mix, especially in the low end of the mix, where boundary cancellation, etc. can screw things up.
Listening to some of your favorite recordings on your system can help you learn the nuances of your monitors and room, thus helping your own mixes.
FWIW, my budget Mackie MR5 monitors (which i like, but i'm definitely no Mackie guy - I got the pair used on eBay for $235 shipped!) are spec'd at 60 Hz - 20kHz +/- 3dB and there is a 12dB/oct HPF @ 60 Hz before the LF amp to help prevent over excursion. I've just learned how low end translates on them. And I agree, if you truly need the extra low end, a sub would be the route I'd take.