Hmmm....
Certainly - I wouldn't want to confuse anyone here, but I don't think I'd be too harsh on the SB if it's an XFi series PCI unit made in the last few years. Some of these units have specs which actually outdo some well known 'pro' brands. I'd quibble with an XFi's mic/line input, no doubt, (although digital in would be fine) but its output is
way more than suitable for driving a set of monitors. I've used them in the past (I had an XFi Extreme Music) for a time and their ASIO interfaces worked fantastically (plus they had no-cost DSP based effects you could drop on a monitor/headphone mix - it's based on E-MU technology after all). Creative also endeavored to update it's drivers to Vista and Win 7 as well. For myself, I'd put a more confidence in their ability to produce well-written Windows ASIO drivers than a company that considers a PC internal interface product a niche item.
I would agree with a PCIe recommendation for new equipment, but I don't really see that using an existing PCI interface, at this moment, as much of an issue for audio data. Within reason, there is just no way anyone is going to 'overload' an PCI interface with audio data, nor is the the bridging from PCIe to PCI going to have any real impact.
What's key are two things; the quality of the interface drivers, and the quality of a DAW's internal scheduler for mixing and and effect processing. Unfortunately, we're limited to subjective observations here - we have no proof other than what we see/hear.
Personally, I'm not crazy about Realtek. They could easily have better specs. In a perfect world, motherboard based sound chips would be ideal for monitoring. But we're not, and we as music and sound oriented folk have greater needs.