Hoping to breathe a little bit of life back into this thread by posting a few bits of new info.
Starmate 5 has a 12 pin header that looks like jtag above the RAM chip, I will work to get the pinout for that sometime in the future (I've got 14 of these radios lying around)
All ST1 generation receivers (Starmate 1, Brix, Streamer GT, Sanyo Dish, XACT 1) have the same can/transceiver board. I will post an image with jtag pins labeled as soon as I get my pentax K-X
Currently working on a Sportster Replay / Sportster 1 (Nearly Identical boards), RX + TX pins give garbled output (baud?). Radio is stuck at sirius statup image when I access UART.
Sportster 5's have a JTAG port under the ARM chip on the left side of the board. It's a 14 pin header, someone should trace these pins since the ARM schematic is available.
I'm currently working on a starmate 2 (I've only got one chance with this).
-- Notice for the CAN boards. The Atmega chip DOES NOT hold anything related to activation, it's all held in the TSOP. I've been successful with a TSOP swap using hot air.
And those of you that have tried out XM hacking, don't give up. It's a hell of a lot easier than you think. XpressRC & XpressRCI use TSOPs, and I've done a successful swap.
Also, to the person who had the "Acquiring signal" issue with a radio, reflow it and it will work again