Assuming you have a 2-fan Antec TP, and it has no coil whine, it's a decent PSU, with separate lines for the 3 main voltages. That's actually better than a Nexus, which has a shared 3.3 and 5V line. (They are not independent)
Either the 80mm or the 92mm fan can be replaced, and the remaining fan removed. If you remove the 92mm, you my want to consider blocking the hole so the intake air is forced across the lenth of the PSU HS, although with the small intake vents on that side, you may see a bit higher turbulence of reduced airflow...
The control circuit feeds the fan an exponential curve as internal temp rises. If by changing the fan you drop the airflow from say 20 cfm minimum to 12 cfm, then the temp will rise a bit quicker under load and the voltage to the fan will also rise a bit quicker. Under normal loads I would guess that your lower cfm fan will vary 5~8V, but assuing you have something close to a Panaflo L, it will always be considerably quieter than the original, especially as you will have only one fan. You will have an idea of how much the lower speed fan will speed up by noting how much it speeds up with the stock fans now: do those stock Antec fans rise above the detault 5V? How often? Easy to tell by monitoring the fan only output voltage.
The heat will rise more in the PSU -- maybe to as high or higher than would be the case in the Nexus. Keep in mind that MOST if not all quiet PSUs with low fan speed at idle/mid power have a bit higher temps. The idea is to use the temp headroom that's available under such conditions. Like let's say VR transitors in the PSU can work at 5-90C. At idle in the typical PSU, maybe they run at 40C. Reduce airflow at idle and they go to 50C. So what? Far from max. Now when the PSU is pushed to the top, maybe the part will reach closer to 90C faster than with higher airflow fans.
Does it matter? Maybe in the long run (how long will the PSU last), but unlikely in the short unless you pin the PSU at max for long periods (10 minutes+), which in my PSU testing/measuring experience, is very tough to do in non-lab conditions. Almost impossible.
Anyway, lots of people have successfully replaced one of those fans with a quieter one, and removed the other. No question it is quieter than before -- and cheaper than buying new. But if you don't want the hassles, go ahead and buy a quieter PSU, sponsors and advertisers will be happier.