So I was wandering if there is a way to get the 396xt and the 996xt to pickup encryption like the DES / OFB? The 436HP & the 536HP both picks it up but when I put it in the 396xt it does not? Anyone know if its possible to make this work on the 396xt or the 996xt?
No.
Some scanners will play garble noises or static when receiving encrypted transmissions and others will mute encrypted transmissions, but no scanner will actually decrypt an encrypted transmission. If you're hearing intelligible audio on a scanner, the transmission is NOT encrypted.
The whole point of encryption is to make it mathematically impossible to recover the cleartext message (whether words, images, video, or audio) without having the decryption key.
If you're hearing intelligible audio from a x36HP scanner but not from a x96, it's probably P25 Phase II TDMA or some other digital format the x96 cannot process, and that has NOTHING to do with encryption.