There are two approaches that I can think of:
1) Use oa2cdb to migrate the design database back to CDB, obviously you will lose any OA-specific features, but this may not be such an issue for a schematic.
2) Use dbWriteSkill() to output the schematic design in IC61x and then try to load this in IC5141, you will want to give the release appropriately for the IC5141 version for the t_release argument (not sure how this needs to be set, my guess is "5.1"):
[ g_ref ]
[ g_lppString ]
Good luck whichever method you choose.