Page 2-25 of the A8N-SLI Deluxe manual contains a Power Requirements
table. It says 12V @ 17A minimum on the output of the power supply,
for a pair of 6600GT. An Antec Truepower is 12V @ 18A, so it just
squeeks by. The Asus table says 350 watts total power minimum, and
the Truepower is 380 watts.
The 6600GT draws 4 amps from +12V:
http://www.xbitlabs.com/articles/video/display/geforce6600gt-oc_3.html
Whether the 3500+ is enough to drive the two cards to max power
is a good question, so they might not make it all the way to
4 amps.
A quick power calc:
http://www.amdcompare.com and list Athlon64. Check the part number
for your processor and see if it is 67 watts or 89 watts. At
89 watts, your +12V current is 89/12 * 1/0.90 = 8.2 amps at
90% efficiency conversion by the Vcore circuit.
Processor 8.2 amps (less if it is the 67 watt processor)
Video 2x4.0 = 8.0 amps (CPU limited most of the time, so <8 amps)
Disk drive = 0.5 amps
Fans 1.0 amps (or compute the exact number using fan labels)
Total 17.7 amps
The reason I didn't include the DVD, is you aren't likely
to be burning at the same time as gaming. If just reading
a game CD, you might throw in another 0.5A for 12V. Good data
is not available for most optical drives.
Modify the above calculation as you see appropriate
Paul