Onboard Audio vs dedicated sound card

[Gamevet]

My current setup is a 650 watt power supply with three GTS 250s set in 3-way SLI mode. The 550 Tis have less power requirements than the GTS 250s (110 watts vs 150 watts).



That's mine as well. LGA 775 socket with the exact same Realtek chip.

Why not just get a GTX 560 Ti card? It blows the doors off of a 550 ti, overclocks very well and is only about $80 more. The price of (2) 550 Ti cards is going to be more than the single 560 Ti and the performance won't be that much better.
http://www.videocardbenchmark.net/high_end_gpus.html

Are you running a QX9xxx processor? You're probably bottlenecking three GTS 250s if you're using a dual-core or low-end quad. I bottlenecked my (2) GTS 460s while running the Metro 2033 benchmark test; even with a Q9650 @ 3.3 Ghz. It's the first time I'd seen my videocards running at only 70%.