Can a bass-shy / polite tubed preamp be remedied?

If a tubed preamp is reputed to lack some slam in the lower octaves, what mods (other than the usual - rolling of the tubes, and experimenting with various power cords), are generally recommended? Would changing the cheap stock diodes to a reputable brand help? If not, what would?
You may want to contact a builder or designer of this stuff like Electra-Print. I'm guessing some form of power supply mod and inline output transformers would give you all the slam you could ever want.Why not talk to the people that make them directly?

Good luck
To answer tube pre modification part,
adding an inverting unity differential stage may do the trick. You can try it using Musical Fidelity X10 tube buffer which is realy what I mean above.
Changing an amplifier for the higher input impedance(I can only assume you have solid state amp) may also fix the problem.
If you live close-by, I can lend you my X10 so you can see if the problem is fixed. There are also cheap differential inverters(in $40-ish range) could be purchased at the pro music/audio stores so you can try it, return it back and shop for the product of a higher quality or mod your preamp.
Marakanetz, The Musical Fidelity X10 tube buffer sounds interesting. Do you live in the NY area?