It is a symmetrical amp. Maybe your unit has been previously used in monos with no bias matching up. Based on your info, as well as, one side is warmer I think It will need to be adjusted in bias. I suggest to send an email to the Burmester Customer Service: email@example.com
Thanks everyone, I talked to the burmester USA rep, and they told me that a 20% difference is ok, but will eventually need a bias Tuning. They also told me that this is necessary between every 5-10 years depending on the area and load the amp is under. We discussed that the next time the tech is in my area for servicing that they would schedule me in for a bias tuning.