Eugen,
The body woods are Quilted Maple top and back, Maple core, Purpleheart accent laminates.
The neck woods are Maple and Purpleheart with Ebony fingerboard.
Ed,
The 20th Anniversary electronics are similar in that there is a separate filter (and preamp) for each pickup. The 20th Anniversary uses 2 individual volume controls instead of the Signature's volume and blend controls. 20th Ann adds the stereo/mono output switch.
Overall, I've found the Signature electronics to sound slightly more midrangey compared to the 20th Ann. Some people find 2 volumes makes more sense than the vol/blend of the Sigs. It just depends on what you're used to I suppose.
Also the different scales and woods of the two basses will make an impact on the tone.