The optical out is probably audio only, and that may be some unusual form of audio stream, so it's best to stay with the analog audio unless you can demonstrate the digital stream works right. Laserdiscs are analog, not digital, so the few that had digital audio out were pretty weird, format-wise. Some discs had digital audio streams, most did not so that digital stream may be dead if the disc has analog audio only.
The SVHS is your only option for video. If you have a lot of these discs to do, consider buying a good DVD recorder, as your PC will be tied up for many many hours doing captures and conversions, and you will tire of it quickly. Also be aware that Laserdiscs did not have anamorphic images, so they will all be 4:3 video, letterboxed.