GXW4108 and Trixbox

I'm using 2 GXW4108's in a Trixbox CE 2.6.1.2 configuration. I have a few questions:

1) Are there any special configuration settings I should be making? I'm using the recommended one stage dialing method. The manual states that "Use Random Port" should be set to yes if using multiple GXW410x's behind a firewall. Inbound Callers are reporting that sometimes the phone just rings and rings, even though the phone service provider tells me that if all phone lines are in use, the caller should get a busy.

2) Each of the GXW4108's report one FXO channel "Line X: busy, PSTN Incoming (CID): unknown" on the status page, even when no activity is on that channel (or on the phone system). Does this mean the FXO port on the GXW4108 is no good?

3) Some users are complaining about callers sounding "Crackley". Should I adjust the Rx gain?

4) In the FreePBX Trunk setup, a maximum channels field is available. The first GXW4108 has 6 Verizon POTS lines plugged into it. If I set the maximum channels to 6, does Trixbox take outbound calls into consideration when determining this count?

Thanks