Okay, I've done quite a bit of experimentation with this.
There are 4 prom versions that I have been able to get for the DTivo.
1.84b, 1.01, 2.03, and 2.05.
1.84b does not support dual tuners and looks more like a SA prom. It does not load the ramdisk. It will work with 2.0 and 2.0.1, but you must edit the rc.sysinit becasue it will cause the kernel to panic when the irprog program is run. With 2.5, it does not work correctlly because it does not support the dual tuners.
1.01 is the prom that is located in the prom directory on the 2.0 software. It does kernel checking and loads the ramdisk. It also supports the dual tuners and the beta version of 2.5 will work with it. I don't have the final 2.5 yet.
2.03 and 2.05 seem to be very similar. I have found no differences in the boot menu on either of these. They both work just fine with 2.0, 2.01, and the beta 2.5 that I have. They both do kernel checking and load the ramdisk. They also both support dual tuners.
Information wants to be free....