I assume your Integra ECU is a PG7.  I have an 89 Integra PG7 in my CRX with my ZC engine.  I wouldn't put back the SI PM6, because the Integra ECU has more aggressive timing and fuel maps.  It will simply work better with the ZC engine.  If anyhing, I would love to get my hands on PM7 ECU, which is actually made for the ZC engine, but they are expensive and rare.  I was also told that if you chip the SI PM6 ECU, that PG7 will still work better.  I'm not 100% sure about that.