I'd just use HDMI from PS3 to TV, and optical from PS3 to amp.
You could route the PS3's video *and* audio via HDMI through the amp if you wanted, but I don't think there's any real benefit though.
---------- Post added at 22:42 ---------- Previous post was at 22:36 ----------
Actually, thinking about it, I'd go with BenMcr's suggestion.
I was initially thinking there's no point of routing through the amp via HDMI as it isn't a 7.1 HD amp, so you may as well just use optical for the audio.
But, due to an annoyance with the PS3, there is a benefit still though:
The PS3 can only output audio via one output at a time: e.g. optical *or* HDMI.
This means if you have the PS3 hooked up to the amp via optical & the TV via HDMI, you need to go into the PS3's audio output settings everytime you want to switch from HDMI audio (TV speakers) to optical audio (amp) & vice versa.
Routing it all via the amp using HDMI would avoid this:
The PS3 would just be left to output audio via HDMI, then if you wanted to use the amp you turn that up & the TV down, and if you wanted the sound from the TV you'd turn that up & the amp down.