Even if you can’t rencode video, you should be able to mux together the DVD-5 video with whatever video and subtitles you choose and make a DVD-9. Use PgcDemux and tsmuxer to demux the DVD-5 and MKV. Then use Muxman to mux it all together to a new DVD. You can get standard-def subs from Project Threepio.
Oh, and if you want the isolated score for Star Wars in lossless, PM me.