Is it possible to just buy the 'banana / rca (male cable)'?

I tried buying just the RCA attachment and they wouldn’t sell it to me. They sell it only as a complete set.

The longest is 12-inches (RCA male) and the shortest is 6-inches

Would there ever be a need or reason to connect the source device > idefender+ > usb to rca cable from groundhog+ > ac ipurifier ground port?

Hi! The iDefender is designed to remove the ground connection. The groundhog is designed to add a ground. There shouldn't be a situation where you would want to remove then immediately add back the ground connection. I hope this helps. Tiffany

I have an 11ch amp w/ 2-prong power w/ xlr's and speaker binding posts being the only open ports. would the groundhog work to reduce hum from the amp?

If a missing ground is causing the hum, then the Groundhog would be the correct solution, but you’d need an open RCA or 3.5mm port. If you don’t have any ports available on the amp, then you can try using the Groundhog to ground your audio source.