Yamaha Tyros, PSR2000 & PSR2100 Owners!

Please help !:

I've created some midi songs using my Tyros keyboard's onboard sequencer.These songs also include auto accompaniment chords recognized during recording, of which are then stored as part of the midi file as Yamaha Exclusive 'XF' chord data. As a result, when the midi sequence is played back, the chord changes are both displayed in the Tyros' Main Screen's 'Chord Window', as well as sent to the Tyros vocal harmonizer to trigger correct backup harmonies. In addition, the vocal harmonizer on/off status is also stored in the midi file. The advantage of having both 'chord change' & 'vocalizer on/off status' data incorporated into the midi song is that it allows you to play back the midi file on the Yamaha sequencer and simulataneously sing along to the song, automatically triggering the correct vocal harmonies, as well as having the vocalizer turn on/off at appropriate spot(s) in the song.

Ok, so far so good, but in addition to the above, I want to also be able to play the keyboard live (Panel Voices: Left, RT1, RT2, RT3) while the midi song plays and sends XF chord change data to the Tyros harmonizer to trigger vocal backup harmonies.

My PROBLEM:

When I play a Tyros midi sequence which contains XF chord data, and then simultaneously play the Tyros panel voices (Left, RT1, RT2, RT3), the Tyros recognizes the chords I play live instead of the chords stored in the midi sequence. This happens regardless of whether the ACMP (auto accomp) button is on/off. Apparently, chords played live supercede the XF chord changes in the midi file.

Is there any way to get the keyboard to 'ignore' the chords I'm playing live and instead, 'only' recognize the chord changes stored in the midi file? If so, exactly what do I need to do to accomplish this?

Btw: I experience the exact SAME problem on both the PSR2000/2100 as well as the Tyros, so input from PSR2000/2100 owners, as well as Tyros owners would really be appreciated.

Thanks in advance,

Scott