the UX8 is a very different beast vs the octane if you consider the add ons.
I think both are 8 in/out interfaces but with diff brands, there are of course various design differences. The octane I've read (in their mktg brochure) that it has award winning mic preamps. But don't mistake this as a main replacement for those studio mic preamps that go for hundreds to thousands of dollars. But Like any other high spec model interface, the preamps on those are up to the task of course in doing your recording needs. The preamps we were previously discussing in the thread are the modeling preamps on the ux8 not the onboard hardware preamps. the octane has lightpipe so that's one for maudio.
Same thing with the UX8 close to features but as I mentioned before in the thread, their converters might be nicer. I'm guessing from what I've read and its added bonus is the whole pod farm platinum which comes out as a great bargain seeing that you have an interface PLUS the complete suite of line6 amps fx etc without having to buy a pod xt or something.
Where their difference lies doesn't speak for what is a better product but maybe what your needs are. I was looking for a nice line6 package with the modeling integration and the ux8 fit the bill for me in terms of features and bang for the buck but if you're just after the interface features, the octane can of course be a contender