Just found the RC9500 service manual for download, and this decodes the suffixes as follows
/N1M - EUROPE
/TIM - UK
/A1M - AUS
/U1S - US

So it does appear that I have a US model , and therefore need a US RF receiver (RX7001 or RFX6500). Oh well, back to eBay.

Thanks all for your comments.
Richard