DX200 base unit connected to a Tecpro / ASL PL system with low level audio in / out of the base unit to the Tecpro/ ASL PL system 
Tecpro / ASL  stations are completely compatible with Clear-Com stations. However, Clear-Com stations have a lower bridging impedance and hence this can lead to audio issues.
There are number of options for the customer to try 

Option #1 (recommended) TP has a higher impedance than what the DX200 is looking for – 300ohm vs. 200ohm.This makes it difficult to null the interface, which can affect the audio levels. Users will often terminate the DX200 base in order to reduce the echo caused by the mis-matched impedance – many times the null is better with the DX200 termination on, but you will notice a significant drop in audio level caused by the (improper) double termination. 
The DX200 is set for a 0db level on the two-wire I/O. This can be adjusted internally at Pots R46 and R57. The user must be careful though as the pots are set close to the max level before a very noticeable increase in the noise floor of the system. R46 adjusts the receive level for the 2-wire and R57 will adjust the send level of the 2wire.

Option # 2 Is to use the 4wire connection from the DX200 basestation and couple it to a Tecpro 2/4 adapter like the AD903  

Option # 3 Set the Techpro / ASL termination to ON, inside the DX200 set the PL termination ‘OFF’ & then reduce the level of the DX200 transmit audio using the internal pot R57 The input level pot shouldn't be changed.

However most customers - prefer option #1 
The good news, is that the DX210 (which replaces the DX200) solves all of this with the auto-nulling and external two-wire adjust features.