You can use the BG6000 QUAD as a regular stereo record player without the quad capability, by just selecting the CD4 switch to OFF.
The sensor for the 30kHz CD4 carrier signal is thus disabled, and only the stereo RIAA function of the preamplifier will operate.
Think of the 6000 as a 4002 with one extra - the built-in RIAA amplifier.
If your main amplifier already has a phono-stage RIAA preamplifier, then there is no reason to buy a 6000; the 4002 without the RIAA amp will be just fine.
Menahem
Learn from the mistakes of others - you'll not live long enough to make them all yourself!