I tried the Line Out into my PODxt with no sim, but a speaker emulation. It sounded awful. ;) THe Marshall JMP Speaker Emulation thingy-ma-bob is supposed to be a good, but it's more expense... :(
It's a real shame that THD (or any other attenuator manufacturers for that matter) didn't put a speaker sim in the line out, but there again, it'd bump the price up even more. Using a mic up against the speaker is still the best way to get your tone onto tape, the HotPlate lets you do it at a more bearable level...