Eirik,
I finally got around to this project, and you were right; PRF.ENDCAUSE was 249 'Modulator underflow observed.' I changed PRF_PKT_CONF from 0x6(SmartRF's value) to 0x0, turning the tone off. Now it works, my chip is communicating with SmartRF's packet RX program.
As a follow up question, the manual states the tone is sent in front of the preamble to "resemble one of the other vendors." So why does SmartRF enable the 'tone in front of packet'? It would seem unnecessary because SmartRF is for TI parts, and not "other vendors."
-Fred