I don't think the sound card is your problem, I think it is probably system configuration, however I'm no cubase expert.
For my money, I went for an RME Audio Digi 96/8 PAD. Fantastic card, lovely A/D converters, S/PDIF IO etc (400 USD). For Midi you need a separate PCI slot and a different RME card hence the soundblaster for Midi and system sounds /mp3s.
In terms of sorting out the latency issues I suggest going through the literature that comes with the progs / sound cards very carefully. It is a pain in the ass but will probably get you there eventually. I ended up fixing my latency issues by changing the priorates given to music stuff in system settings. Works like a dream but means the computer has to think about where the mouse is.
Or you could ask the folks at
home recording dot com . This site is some times a bit of a war zone but if you persevere can be useful.
My
instructors page and
www.studiotrax.net for all things recording.
my toons Brought to you by Dr BadGAS