Hi fvang,
1. The EP 350 IS a "subwoofer with a built-in amplifier" so you should be just fine connecting it to that jack.
2. Nope.
3. Just measure the distance between the center of the positive (red) post, and the center of the negative (black) post on one or your receiver's speaker outputs.
The Axiom bananas are 3/4 inch from center to center. If your receiver's posts are 3/4 inch apart, center to center, the Axiom dual bananas will work just fine. If the distance is not 3/4 inch, you'll need to use the single bananas. Axiom offers those also.
