How much of a difference will a dedicated DI box make?

I'm surprised no one mentioned the Redeye 3D unless I missed it.
No, you not missed it. Redeye 3D Phantom costs more, thats the "reason" to exclude, of course you will have additional reamping device... but you will need interface with serious output level for that :)
As I`m remeber from one of test J48 was not so great against countryman and ordinary redeye (not phantom), except the case with passive pickups where redeye was no so great due to impedance.
 
^ That article was an excellent read, thank you.

To the poster asking about the UX2, I use this interface too. The UX2 has Hi-Z inputs, along with a pad input for active pickups, and I have read in this forum that this should do the trick without needing a D.I. box. The article linked by Terminus will be of great help to you. I use some of Pod Farms pre-amps and its compressor to make D.I.'s. (Then pod farm is never used again in my recording chain lol) But I will be the first to admit am probably doing it all wrong!!
 
96k will not help with toneports because of samplerate limitations (up to 48k) :)
96k only through resampling, so no gain in quality.
 
Thanks a lot for everyone´s input!

The conclusion seems to be that a DI Box won´t make much of a difference if your Audio Interface has good enough specs.
Also there appears to be no contender to EMU 0404USB in the same price class.

So I´ve decided to keep my interface and get a Radial J48 in order to split my guitar signal, one direct channel with amp sims, and I´ll put an SM57 in front of my practice amp. So far it does seem to add somewhat of another dimension to my guitar tracks.