I'm gettin weak bass and dynamics in one speaker

Swapping speakers cables is a lot more pain and effort than simply swapping IC connections on preamp from the source or to the amp.

Start first by swapping speaker cables left to right. First thing to do is make sure its not the speakers. Then if its not the speakers, you can isolate the problem by ways mentioned above.

Start at the source end and swap the L and R interconnect connections and see if the problem changes from one speaker to the other. If the problem does not move from one speaker to the other, move on to the next piece of equipment. This method will allow you to isolate the offending piece of equipment. Once you isolate the problem and if the item is tubed based, swap the tubes from left to right to isolate the defective tube. Good luck.

It could.

Swap in a spare and see.

ITs good to keep some inexpensive but decent SS gear around as spares for regression testing when needed. OR even just spare tubes in this case. ANything to help make a quick swap and isolate where the problem is.