You will be alot better with a external channel bank that with a gateway with many interfaces for e and m.
The channel bank is normally more robust than a gateway to handle the voice in aplications like that.
On channel banks ,you have two types.
1)Cheap, old and bulky. Designed to stand bullets, telco style channel banks
2)Sleak, small, smart and expensive.
You may whant to consider a smart channebank that will do “silence” or voice supervision, in case that those trunks have troubles with the supervision/disconection.