Create another sheet that uses the same data source and filters.
Then display the stuff you want to display dynamically in that sheet's TITLE.
Text boxes only see parameters, not data source fields. But the sheet will see it. Just hack up the title the way you envisioned the text box looking and run with that.
Oh, and as for any data that the sheet may want to display, you can just float that section of the sheet behind all the rest of the stuff on the dashboard. (Or, rather, float all the rest of the dashboard objects above it.)
It is possible to achieve what you are looking to do, though it will take a bit of work.
There are many different ways you can approach it, using titles, multiply sheets, etc.
The link below shows you how to make a title dynamic, but don't just stop there, you can also do this within the sheets themselves.
Hope this helps you get started.