What version are the OAS/MGI cards? Should be 2.05/1.30
What version are the LP40 card(s)? Should be 2.04
What version is the TEPRIa/TEPRI2 card? Should be 4.28
What codec are the handsets configured to use? I'd use G.711

There are syslog traces you can get from SMT-i60xx handsets these might help

4.92 was the first release to support the SMTi-60xx handsets, might pay to upgrade to 4.98