I just checked my PSR9000 and yes, you can add separate solo tracks to a previously sequenced EASY RECORD type recording - without first saving the sequence.
All will become clear when you get your PSR but what you do is:
1) Perform your APC recording using EASY RECORD.
2) When complete, press STOP and press the PREV button twice - this will take to the recording type selection screen.
3) Select MULTITRACK RECORD and you can now add more tracks to your sequence..