The Envoy and Aria are my absolute 2 favorite spas from Hot Springs so there isn't any negatives in my opinion
Personally though I like the new "regular" cabinet style versus the NXT but that is a subjective opinion. You'll see a lot of nice upgrades from your old Grandee: redesigned jets that you can completely shut off and also swap around with each, new easy to use control head, ACE Saltwater which is a nice option, new pillow design, new zoned lighting, new colors, etc.
I'm not a huge stereo guy but I will say the Bluetooth w/ Subwoofer option sounds pretty dang good