Already some good responses. Whenever I have had a problem which is different in the L-R channels I start at the source (in this case the Rega) and swap the two channels, and see if the problem reverses at the speaker. If not then I put the connections back , move one forward in the signal chain and swap again (the very last swap is the speaker cables). This will tell you where the problem is (turntable, phone, main amp, or even speakers) : it's whatever is driving the last cable you swapped. For example if swapping the cables between the Rega and EAR makes no difference, but swapping the cables between the EAR and the bryston alters the volume balance between the speakers then the problem is with the EAR.
Another very quick and easy test in your case would be to get a CD player (perhaps with a variable out) and connect it to one of the inputs of the Bryston amp ... if it sounds fine then the problem is somewhere in the phono chain, if it sounds awful then the problem is most likely in the amp and speakers.
The previous comment about NOT plugging the EAR into the phono input of your amp is also a good one (though I'm not familiar with your amp to know if it has a phono stage ... if it does then perhaps try plugging the Rega in directly .. this would be another test of the EAR).
Hope this helps.
Another very quick and easy test in your case would be to get a CD player (perhaps with a variable out) and connect it to one of the inputs of the Bryston amp ... if it sounds fine then the problem is somewhere in the phono chain, if it sounds awful then the problem is most likely in the amp and speakers.
The previous comment about NOT plugging the EAR into the phono input of your amp is also a good one (though I'm not familiar with your amp to know if it has a phono stage ... if it does then perhaps try plugging the Rega in directly .. this would be another test of the EAR).
Hope this helps.