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 athome recording dot com . This site is some times a bit of a war zone but if you persevere can be useful.