DMX 512 transients

Hi everybody.

I'm developing a DMX512 receiver and have some doubts about grounding and transients protection.

This is the receiver scheme:



Input and output follow floating topology for DMX receivers.
Vx And Vcc are isolated supplies (each one with its trafo, rectifier, etc).
D2, D3 and D4 are bidirectional transient supressor diodes.
All grounds in the system but XGND are tied to chassis ground.

For transient protection, I've followed this scheme(found in a TI appnote):



It uses a grounded topology, with bus shield tied to system GND, wich is not recommended.
I don't know if I should tie TVS diodes to XGND (as shown in the first image) or should do to bus shield (pin 1).

Thanks