RT-AC68P (with upgraded CPU, NOT R or U)

I went to buy an RT-AC68R at Best Buy today, and instead found they had the RT-AC68P (with a dual core 1GHz CPU) for 20 bucks more. I have seen this called the RT-AC68 v2 elsewhere on the web). I have started playing with it and successfully flashed Merlin's latest build to it. I have, however, been unsuccessful getting Shibby's Tomato firmware installed. I've tried both the recovery web UI and tftp methods (I'm on a Mac with no Windows machines around), with no luck.

2 questions:...

RT-AC68P (with upgraded CPU, NOT R or U)