Thank you for your post and welcome to the Bose Community!
In regards to your query, as the Wave system is not designed to be used with a TV. The only way to connect to a TV is by using the AUX port on the back of the system. This port also needs to be used to plug in your Echo dot as well. You may be able to find a 3rd party splitter for the two sources. However, please be aware that this may alter your Audio quality through the Wave system. I have included a LINK HERE to Amazon to give you an idea of the splitter you could use.
I hope this helps! If you have any other questions please reach out again!