well fxpansion claim that the wrapper does not add any delay and the cpu load is the same, so in other words it works just like it is ment to.
for your question on what system would be better, depends all on your needs.
both pro tools and cubase are good there will be no big ddifference btween the 2 with sound quality. if you will be needing to use midi more then cubase might be the choice as its midi is alot better than pro tools, if midi isnt needed as much and you will also be doing alot of recording with instruments then pro tools would be the go.
with the m box you will have 2 mic pre amps and the m box will be your souind card and the pro tools software comes with the package.
with cubase you will you wil have to get the program and then you will need to get a good audio card with the i/os you will need, and then you would need to get a mic pre, if your wanting to record instruments.
if you got cubase a soundcard like
the delta 10/10 and a personus blue tube pre amp, you would have the same pre amp inputs there and some would say
the blue tube has better pres than the m box and then some would say the m box would be better this is all personal opinion now.
you can get the 2 packages to offer the same thing price will be a differnce you would spend a bit more with cubase and getting the pre amp but would have some more i/o depending on your sound card. after price the differnce is the software, pro tools have a free version of there software which limits you with ariund 8 audio channels but gives you an idea of how it all works, not shure if cubase sx has a demo if it dies try it and see what program you like the best check your money then go with what feels the best with you.