There are adapters from HDMI to optical but that won't change anything for you since the SPDIF connector does not have functionality to control volume this way. You can stick wings on a dog but that won't teach it to fly.
Or get a remote like a lower end Harmony that can be programmed for several devices without multiple remotes. Although for a 37" 720 TV that still had S-video inputs upgrading is not a bad idea, especially with the prices for 55" range TVs now. You can even get a used set much newer than yours for under 200.