I also have a C521i. And a Delta66.
I find the E-mu to be head and shoulders above it. The DAC is a CS4398, and the card is professional grade. I've spent a lot of time in studios and demo rooms and the players that (I have heard) can beat it are Wilson Audio separates (Transport and DAC separated, cost >1 lakh) and a Lynn player that cost about 2.5 lakh. Not the C521i, the 541i, or the Cambridge Azur C540. I haven't mnaged to audition more players than those, but I think the E-mu does just fine.
I probably used the wrong term - it's a studio audio interface, not a sound card. It has two analog I/O, the rest of the ins and out are served over AES/BU and ADAT. It's not really comparable to a 'sound card' in the way we know it.
Not that it can't be improved upon. The Lynx Two has better analog circuitry, and is yours for only about US$999. The card that comes very close to it, and for a bit cheaper, is the Juli@, but the analog section is a toss-up. A good DAC with the Juli@ puts it in a class above the 1212M, but then I'd rather go for the Lynx.
IOW, yes, I think I'm happy, and I think the next level of performance is significantly more expensive than what I bought.