You will have MUCHO difficulty with the SCH2P as there is no good way to eliminate the retransmits that the tuner will do as you cannot respond to the tuner quick enough (< 100ms) to satisfy the lower layer protocol retransmit threshold. What this means is that you will likely get the same response packet 3 times for each request you send.

Furthermore, whenever you send using RFX9600, the incoming serial buffer is cleared. Therefore, if you had any data in the buffer (asynchronous events or the other 2 copies of the response packet), you mayl find data is gone or corrupt in cases where you cleared only a partial packet.r.

I worked with Sirius early on as they asked me to write a module for the Pronto/RFX9600. I had something working but it wass nowhere near robust enough (meaning that there is too much room for errors to warrant a stable/reliable/performant module) and finally threw in the towel after discussions with Belgium and Sirius. I am waiting for the new controller to try again.

My suggestion, put the SCH2P behind Netstreams or a Sirius-Ready receiver.