I Need Help with a Passive Sub

a quick lowdown on my system,ALL MCINTOSH,c-38 preamp,mcd7007 cd player,mr7082 tuner,2 mq101 eqs 1 for each amp,cary cad 5500 tube dac, mc300 amp,mc 7150 amp,1 pair klipschorns,1 pair cornwall 1s, the mc300 for the cornwalls,mc7150 to the k-horns,here is what im trying to figure out,i have tons of bass but its not full & rich just kinda hollow bass,im thinking of adding atleast 1 maybee 2 passive front firing subs to be powered by a mcintosh ss amp, i have plenty of bass directed at the floor with the k-horns so im thinking front firing,any ideas?
The big VMPS subs are passive and front firing. They are easy to drive and go very deep. I'm driving mine with an Onkyo M-504 amp crossed over at 35hz.

I think you may need help with the room acoustics. Your speakers will rival any sub made! You may want to bi-amp or bi-wire the khorns? Put different feet on them? Try a different amp on them? Remember that low bass will use the majority of your power. However, your other problem here is that, at least in my opinion, mac tube gear sounds better than mac solid state.
Try going to 1 pair of speakers and using the cornwall amps to biamp the khorns. You may get a nice response.