This odd catalog numbering system that Crash mentions seems to be the standard for Apollon's 2-disc releases (APCG-900X). Basically they use a main cat. number for the entire album and then sub-numbers for each disc. For example,
APCG-9001 has sub-numbers APCG-9001R for disc 1 and APCG-9002R for disc 2. And
APCG-9004 uses APCG-9005R for disc 1 and APCG-9006R for disc 2.
Since these three seem to be the only releases with an APCG-900X cat. number that we are aware of (not counting the
Soul Calibur soundtrack which was released years later by Bandai), we end up with the following list:
APCG-9001 (9001R, 9002R)
APCG-9002 (9003R, 9004R)
APCG-9004 (9005R, 9006R)
This also pretty much proves there was never a 'APCG-9003' released, perhaps it was an intended release that got canceled or something?