This is the Axxess AXM50-GM1 General Motors MOST50 Radio Replacement/Amplifier Retention Interface.

Axxess AXM50-GM1, Select GM MOST50 Amp Retention Interface

Vehicle-specific add-on amplifier interface for use when replacing the factory radio, such as with Metra’s dash kits. It is designed to retain the BOSE amplifier in select GM vehicles. This interface will also retain the balance audio feature when replacing the factory radio and is Micro "B" USB updatable.

Features:
Add-on amp interface for with Axxess interface AXGMLN-09
Retains the Bose amp in GM vehicles
Retains balance
Micro "B" USB updatable