So, a blow off valve and a diverter valve ARE NOT the same thing. Neither have anything to do with the symposer in stock form.
A DV, or diverter valve, redirects or "diverts" unused boost pressure back into your intake system via a small, maybe 3/4" slot machined into the turbo housing (at least on our turbos) located in the piston bore where the DV is mounted. DVs are quieter in operation by design, although if you have an open element air intake it will be louder. It redirects the pressure when the solenoid is commanded open, and snaps closed when under load. See the DV+ video:
https://www.youtube.com/watch?v=3EgXspDfI08&t=1s
A BOV, or Blow Off Valve, vents the same unused boost pressure to atmosphere when commanded open, whether via electronic solenoid or vacuum actuated (in which case, you'll need a few other parts).
A 50/50 set up is exactly that, half recirc and half VTA.
The sound symposer, is simply a box with a rubber diaphragm which vibrates when exposed to vacuum. Useless and detracts from the true experience of the car, IMO.
All that said, there is also the option to remove the complete DV assembly from the turbo housing, remove the symposer assembly, install a block-off plate and CEL defender (at the turbo), install a vacuum reference adapter (usually at MAP sensor), and install a BOV into the hole where the symposer used to live.
There are also options available to install a BOV on charge pipes (CP-E) and on a few intercoolers (none of the factory fit options from most manufacturers have this option).
All in all, the DV+ is very good and robust. Some people experience some trouble with it, I personally have had it installed for 40k+ miles and 2 years of daily driving without issue.
Ron@Whoosh usually has the best prices for the DV+ too!