If you are able to or not i cant say for sure from within this position.
Still the way you explaine is that your possible choosing
rather to upgrade your onboard integrated GPU putting in more
dedicated ram memory?!
Or adding one bigger video card and run that in parallel with Crossfire to combine the two?!
Considering the pro and cons crossfire isnt always the best sollution and for sure not if you looking
for better preformance!
Still if you want to be sure, your not getting yourself something that only half works the way you wanne.
Then take my advice and buy yourself one dedicated videocard!
(Crossfire relies on the chip series im not even sure if it would run if they not match)
Still if that would be incorrect stated crossfire and the idea behind it are great!
Altough theorie and practice are miles from each other.
Anyway remember running 1 / 2.or 3 videocard with extreme high performance ratio in let say SLI will not
boost your Graphics so called overall preformance like 3 times.
That is a myth there is no way to combine them as one just like crossfire it eventually becomes
some what of a problem! I fooled around 5 years ago with that crap and somethings will never change ...