Check out my blog post on DACs and Amps.
I have a PS3 but just use the HDMI audio out into my A/V receiver. I think you can configure what gets sent out the S/PDIF interface, but it's normally an AC3 Dolby Digital bitstream which most stereo DACs can't even decode or use. So make sure you can *always* send 2 channel PCM out the S/PDIF interface and that setting isn't going to mess up using your PS3 for surround gaming and/or movie watching. It might turn the entire PS3 (and all outputs) into 2 channel PCM and you'd lose all surround sound without constantly going into the settings to change it.
If you want optical S/PDIF in that eliminates several of the popular inexpensive choices. You also need to decide what other functions you want (local volume, multiple inputs, etc.).
In general, I'd try to find a DAC with a good headphone output. Headphone amps can sometimes cause more problems than they solve (because many have more gain than you need and also amplify noise--see my blog). So getting it all in one box is likely to work better as the manufacture can match the gain of the internal amp to the DAC, use the proper internal grounding, etc.
Something like the NuForce Icon SPDIF headphone amp would work if you used an optical to coax S/PDIF adapter (which work well and are cheap). But it's pushing your budget at $450.
This would also work, and is cheaper, but I know next to nothing about it as they're not nearly as popular as the NuForce products: http://www.audiophileproducts.com/fubar4
There also is lots or reasonably priced pro sound gear with optical S/PDIF inputs that have high quality DACs. But the headphone outputs are often lousy as they're only intended for monitoring in the field not high quality listening. And most of the devices are optimized around *recording* rather than playback.
Finally, there are some cheap "black boxes" that have S/PDIF inputs and analog RCA line outputs but the DACs and other circuitry in them are likely not great and they don't have headphone outputs at all.
