For me, the key to great Rock & Roll speakers are the following:
1. Great Deep Bass
2. Great low end "Chunk" - think Drop D. or Hendrix on VooDoo child slight return.
3. Great high end "honk" from the guitars with the treble pot turned down, smooth highs, & vocals that cut through all the distortion.
You can achieve this with Tower Speakers with lots of Bass or adding a subwoofer. However, item 2 above my suffer with only a subwoofer supplying all the bass.
Personally, I like towers with bass better than separate subwoofers. It is easier to achieve the best sound for Rock. Look for good size towers with two woofers, the larger, the better. ie. 8" to 10" woofers. Make sure the reviews "rave" about the bass. For the high end "honk" like Dire Straits "money for nothing" and those smooth highs, think "Ted Nugent - Stranglehold", & vocals that cut through, you will need a good quality tower to achieve that. This is where the extra money makes a difference - synergy of the tower. In general, the more you spend within reason, the better synergy you will get and the better you will be able to hear and separate all these great distorted sounds that Rock makes. I hope this helps you.

