Can you play DTS-HD on your old home theater system with a blu-ray player connected to the system.?

No worries! When blu ray was being hashed out, everyone involved knew that there were millions of receivers and home theater all in one systems that would not have the ability to handle the newer HD Dolby and DTS. So, if whatever system you have has a digital coaxial or optical input you will get the legacy dolby or dts even if you choose the HD sound, The blu ray player will pass the legacy DD and DTS over optical or digital coaxial connection. Digitally, only HDMI can carry the HD sound. So I'd just run the HDMI from the blu ray to the TV and run optical from the blu ray to the SS system, just remember to turn the sound off or down on the TV or there could be a slight echo since they won't be perfectly synced usually. There is another option that isn't common, but I use it. I have a very high end receiver that cost 2 grand when it came out back in the day, when HDMI and blu ray were just a dream in someone's head. There's no way I'm buying another high end receiver with HDMI anytime soon. Thankfully, the receiver has a set of multi-channel analog inputs for HD sound which was DVD-A and SACD or super audio CD at the time. With a blu ray player that has a built in decoder and multi channel analog outputs, you can connect the two and hear the HD soundtracks. Not to confuse you, but I mention that just in case you ever have the chance to connect that way. I do and it sounds amazing. I've seen this particular question asked several times, there's only one problem, not all the SS systems have a digital input or multi-channel analog inputs. If you have neither one, there's nothing you can do to upgrade that I'm aware of.