Although you have mentioned that bandwidth is not a problem, a good place to start is to make sure there are sufficient QoS configuration for your two routers connected by WAN and make sure that RTP packets are properly prioritized.
Please see below for LLQ configuration for PPP leased lines or Frame Relay.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...