Usher cp-6381, lacking in bass?

First I will roughly describe my system
Usher cp-6381 speakers
Krell s350 cd player
audio research ls2 preamp
krell kav250a power amp

My listening room is less than ideal I know but it is what it is. It is basicaly the sun room or Florida room and is made up of windows all the way round including back into the house, floor is ceramic tiled. Speakers sit on rugs on spikes on their cast iron bases about 12 feet apart and about 10 feet from my normal listening position.

I find the soundstage and voices to be impressive, however the lower bass is not, what is there is nice and tight but does not seem to go overly low. I also realise the amp is really a home theater amp hence the kav monicker but it was available and affordable...lol.

Room and layout cannot be changed for practical reasons at this stage so what might anybody more seasoned suggest to try and increase lower bass response and punch a little bit?
I mostly listen to hard rock both old and new.
Preamp? Power amp? CD Player, Speakers?
Any or all could be my concern, have had this setup like this for a good 2 years and am happy but just would like to take it to another level if possible without a second mortage!
Thank you