Is bass-expander really good for stereo system?

why not get a subwoofer ? RELs integrate very well, and can be found used for about $800 up. It worked for me. What you're suggesting may work, but may strain your amp and main speakers, forcing them to work harder to drive low frequencies. I'd be very wary as it may be difficult to resell if you don't like it.

I see no mention of upgrade AC cords on your equipment list. That is the very first thing that I would experiment with. You can tune your rig by trying different AC cords; no two sound exactly the same & many differ considerably in terms of their affects on sonic signature. Both the integrated & the CDP could be tuned, not necessarily using the same cords. Buy some used & then turn around what you decide not to keep.

Simon, I would also recommend experimenting with a sub. There are other, (more controllable,) subs such as the M&K line which have a low-pass filter adjustment which will allow you to pick where they compliment your main speakers best. Remember, a sub allows you to experiment with placement in your listening room to maximize your bass response. (Most rooms are corner placed for max bass, in some that is excessive.)

Check this article by Dr. Greene (of TAS) out:

http://www.avguide.com/how_to/bass.html

Good luck,

Charlie

Wow. I just can't believe you are not getting deep bass with the equipment listed above. A tube player, NAD is if anything a bit TOO heavy in the bass, high end cables and a three way speaker? Maybe Bob's got a good idea with the power issue.

Only other main thing I can think of is component isolation, if you haven't done so already. I find the most solid and extedned bass comes from rigid, spiked islolation platforms. Put each on its own platform if you can. I think Needle Doctor has an Apollo brand wall shelf for turntables, but it may work just fine for cds and amps too.
For speakers obviously Target stands are a good choice, however I heard from someone that field point arrowheads from an archery store are a good cheap alternative. (place three per speaker in a triangle formation, one on the front edge, two on the back corners, spikes pointing UPWARD) You may already know all this already but in any case good luck :^)

you may also want to experiment with other interconnects. Try to borrow some demo's from a local dealer if possible. Explain your present sonic signature & your goal of course.