Musical Sub Suggestions

Currently, I'm very pleased with the sound of my system but would like to experiment with adding a bit more to the bottom end. Bass now is well defined, musical but not 'substantial'. This suits me for the lion's share of the music I listen to, but occassionally I get the itch to relive my youth and pull out the hard rock stuff.

I've worked on speaker placement a bit, altough I'm very limited in this regard due to WAF. Most listenning is done in the nearfield anyway. Looking for sub suggestions to mate with speakers listed below. Additionally, I'll need to consider crossovers, so if you have any thoughts along those lines as well it would be greatly appreciated.

system is:
Joseph Audio 7si signature (MKI version) w/target stands
Simaudio I5
Zu Cable Warmouth IC
Zu Cable Julian bi-wire (double run)
Rel Strata III
Subwoofer + musical = REL
In addition to the above statements, I think your wife will appreciate the looks of the REL as well.
One with a parametric EQ built in...It can make a
HUGE difference. It will make any sub more musical
and fast if setup correctly. I dont know if the Rel's
have them but the Revel b15 and Infinity subs do.
And they are both great subs.

Good luck.
Both of the Martin-Logan subs are very musical.
The ACI Titan. Wonderfuly musical
My dealer has the JA sigs with a $1500 B&W sub(can get the model# if needed)...sounds very musical...I do like the "airy" sound of the JA have a killer system...let us know what u went with....REL is also world class...good luck
thanks all for your great suggestions!