New tubes can make all the difference. ask for Andy at www.vintagetubeservices.com You pay more, but you get magic:)
I second the tube replacement.... 1st place to start... There are many available upgrades for this piece - checkout www.altavistaaudio.com or talk to Michael Elliott. His number is on the website... Unless there is an issue with this Pre-amp, the SA7 is not a problem with bass - lived with one for years... What else does your system consist of?
the rest of my system consists of antique sound labs mono blocks- the real small ones, ecl-82 driven at 7.5 watts each driving a pair of NHT super two's. i was using the NAD 705 as a preamp before the counterpoint and bass was no issue even with controls at flat, so i don't think my power amps or speakers are an issue. as a source I am using a rega planar two with a grado silver which i have also had for a while, the only variable is the preamp. the tube change sounds like a good first step because i love the sound and simplicity of the SA7 and would keep if i can improve the bass. its just too loose and undefined right now. it is also excessively noisy which hints me more at tube replacement.
Go for the best tubes you can buy from Andy. You won't be dissapointed. You might consider re-tubing your mono's next. Ask Andy for his advise. I got lower noise floor, holographic sound stage and improved bass extension right away. Everything improved from there over the next month until they were fully broke-in.