1. The OSSC takes audio over the SCART cable, as SCART was designed to carry both video and audio, so there is [generally] no need to include a separate audio input. There are a few approaches you can take to handling audio here:
a. Bypass the OSSC and route audio directly to your amp or TV;
b. Inject audio into SCART at the OSSC end using something like this;
c. Get a new SCART cable from somewhere like Retro-Access that has an audio connections on the console end;
d. Connect audio to the 8-pin DIN and hope your SCART cable is wired for audio; or
e. Ditch your existing AV outputs for a Nintendo AV Multi-out port (pictured here), which includes both audio and video.
2. I don’t believe the OSSC hardware has the capability to buffer audio, so I don’t believe we’re ever going to see audio delay functionality on the current revision. You’d need to either take care of it on your TV, or bypass your TV and run audio straight from the NES to your amp, or look into an audio extractor that can send video to your TV and audio to your amp.