Hi Frank,
it is a myth that you need the expensive audio CDs. Depending on the model of recorder it was possible to load your single blank audio CD, set up your recording while paused. Then use the emergency eject procedure (will vary depending on model) to remove the expensive audio blank and replace it with a cheap data blank. I have made many audio CDs with data blanks and frankly you cannot tell the difference. This is the main disadvantage with stand alone audio CD recorders, if you are limited to the expensive media.

Also with the latest keyboards, recording only stereo, a mixer is really not needed, since everything you need can be achieved in the keyboard mixer and the output level is sufficient. An analogue mixer will only degrade the 6000 output quality.

Also no overload is allowed in digital recording, you should always record a few dB down from maximum to allow for occasional transients too fast for the meters to register. Digital overload is a particularly nasty cracking, quite different to the more gradual 3rd harmonic distortion from analogue tape.

A pc recording system has the advantage of not being limited to expensive media, but a pc is a terrible environment to try and record the highest quality audio. My solution is an external usb soundcard. Here the 24 bit converters are situated right by the keyboard line out terminals with minimal loss in the analogue domain. The usb stream is already in 44.1 kHz format and the wave file appears on the pc hard disk with no quality loss or interference whatsoever. Wave editing can now be done entirely in the digital domain so the pc system used is now immaterial to maintain the original quality.

In fact the best quality converters I have found are in Sony DAT recorders which have a phenominal sound quality. You can record in 48 kHz (which most commercial master tapes are recorded at) and use the S/PDIF converters in the external soundcard to get the wave files for audio CD creation on your laptop, again all in the digital domain with no quality loss.