The only problem with using the U series of signals on a Fire Lite MS-9600 is that (correct me if I’m wrong) since the MS-9600 outputs FWR (Full Wave Rectified) power through the NAC’s, they may not sound the best expecially the UNH/UHN’s. I say this because when I used my Siemens UMMT-S17 on my old panel, a Silent Knight SK-2 which also outputs FWR, it didn’t sound very good.