I am confused with this. My trace 715x combo has an 8 ohm internal speaker. If I plug in another 8 ohm cab the total output is 4 ohms. What is the total ohms if I use a 4 ohm ext. cab? Is it 6 ohms or 2.6? I am told 6 will be OK but 2 will damage the amp. Trace customer service (Peavey) never bothered to answer my emails on this. Thanks for any guidance. I appreciate the help.