When buying HIFI gear at this level it should never need or have to go through a break in period to get it to go from bright, scrill, fussy, boomy or other type of BAD. It should and will go from Sounds Great to Sweeeet.
Check your cables, interconnects etc. If all is good take the new gear back to the HIFI store a tell them you are very concerned something is wrong and need their help. I would hope they respond correctly. If not request your amp you traded in and a refund of your money. Don't be angry or rude as that would serve no good outcome. I hope all works out for you.

