Wow! I recently bi-wired my speakers because I had read that it actually worked really well with mine.
I used banana plugs for the first time, and had to work out what to do at the amp end, which only had one set of speaker posts. So, I stacked the plugs. And, I listened for a while and wasn't greatly impressed. The sound was ok, but it was somehow off. So, this evening I just wired both speaker cables into one plug for each speaker post in the amp - Bingo!! Lovely sound back. Now I get it.
So, yeah, easy and free tweak - don't stack (cheap) banana plugs.