I forgot to add the signal chain. I believe this is what you are looking for.
View attachment 1369607
If you are running these in parallel, you are running a 2.4 ohm load on one channel, which is stressing that channel. The inbalance in channels may also be adding to the overall stress. Even when not running both sets, the 8 and 6 ohm speaker make a 3.4 ohm load, and that probably below the 4 ohm design of the amp.