The Fire Studio Project is Presonus' new version of the Firepod. Again, it does not support sample rates over 96K, and the pres, while good, are not anything special. Given you need one great pre for vocals, this seems like a waste to me. Your existing card has better converters than this or the Firebox.
IMHO you should be looking into a great pre for your budget. Whether it has digital or analog outs IMHO is somewhat (although not entirely) moot, as the converters in your existing card are excellent.