Disklavier

I have successfully produced a CD using MIDI2CD. Simple and elegant. However, I am still stymied by the DK's SRS recording feature. I want to couple my midi files to a commercial CD. I can mate the CD using SRS, no problem, but as far as adding my sequence to the recording it seems I can only accompany the CD. I can re record the track, add a track, but if I edit the file to add my sequenced material it produces a new file. Meaning all of my work on the sequence is now unless, as it will not recognize the CD.  

So, how can I do this?

Thanks

Patrick