Your current BDP will output multichannel via HDMI to your receiver.
The argument for upgrading is only if you want to get a more up to date BDP (and more specifically a UHD with current video processing) and possibly more output options, like analog out.
You can also output audio via HDMI from your TV, if it allows for it.
Your budget is of course a factor. If you want to keep your spend lower, then only invest in the new receiver. The other path(s) are options you could also pursue.
The argument for upgrading is only if you want to get a more up to date BDP (and more specifically a UHD with current video processing) and possibly more output options, like analog out.
You can also output audio via HDMI from your TV, if it allows for it.
Your budget is of course a factor. If you want to keep your spend lower, then only invest in the new receiver. The other path(s) are options you could also pursue.