Cary 300SEI...tube rolling for bass, etc.

[Breakdown7]

Hi guys,
I have Cary 300SEI only a year old (and factory upgraded) that is sounding great, with the exception of bass quantity. I would like to coax a little more overall bass out of the amp if possible. My tube set is as follows...

Output tubes - Genelex Gold Lion 300B
Input tube - 50's Sylvania Bad Boy 6SN7
Driver tubes - WWII era RCA grey glass VT-231's

I am guessing to improve the bass, I should go with different 300B tubes? Just hoping for opinions here, as the unit is already upgraded from the factory with Clarity Caps, Hexfreds, Kimber Cable, etc.

FYI, my speakers are Tyler Acoustics PD15's, which have a relatively flat 8 ohm impedance and are rated to drop down to 38Hz. I have read a lot of good things about the Genelex 300B tubes...just would like a little more bass out of my system.