This past Sunday I bought the Harmony 520 and after two nights and at least 4 hours of trial and error, I finally got my Harmony to operate 3 SA Tivos that are all connected to the same Tv.
The problem was that I was entering the actual models that I have and the remote was being setup with the "0" ir code set for each instead of 5,7 and 9. I finally set it up by claiming they were all the same model so that it would want ir samples from the remote to find the correct code set, which it seems to want when you have duplicate devices. In your case you should be able to setup your Toshiba using a subset ir code and then "teach" it the DVD codes, but as I stated my Harmony remote experience only goes back as far as Sunday, so I can't help with specifics
After trying for about 3 hours Sunday night, I was ready to pack up remote and return it, but now that I have it figured out (for what I need anyway), I already can't imagine not having it.