Doesn't look like your amp supports 5.1 DTS anyway, so my original suggestion seems the best idea.
Supports Dolby Digital on optical but not DTS. One presumes this covers both 2.0 and 5.1 DD, so I guess there is a limited value in connecting via optical (for Dolby Digital Blueray movies and games).
Anyway short answer, yes that switch box will work.
Long answer, you can try Sams suggestion for free and if not happy then buy the switcher!