Yep, the 536HP is faster than the 996XT. Not nearly a 1/2 second though.
Maybe 50 ms or so at the max but enough for a noticeable delay.
Heck, even just 5 or 10 ms delay difference is enough to notice an echo effect. I hate it myself as I often have several radios running and that really makes things sound horrible.
It's too bad they don't offer an audio delay adjustment so you can try and sync all your radios but that may be asking to much.
This is also a probelm with two HDTV's within hearing range of each other, one will decode the audio faster than the other creating the echo effect.
The solution, turn one or both down!
That's not really possible with the scanners though when you may have 7 or so running in the same room.
I try and break up the systems each monitors but many must monitor the same system in order to catch the other active talkgroups. For those, I make an attempt at locking out certain talkgroups so none are duplicated.
Then it never fails where they do a citywide broadcast on several talkgroups and I have the echo. With 7 or more radios running, the different delays can make the audio non intellegible.