The sound of a system is almost wholly determined by the speakers and the characteristics of the room they are situated in. If some packages sound 'bright' it would be due to the speakers or room.
Rooms with hard floors, no rugs, and few soft furnishings will tend to sound a bit 'bright' due to sound reflecting off surfaces, which is the case with my secondary sound system in the room with the TV.
My main 2 ch system is in a room with large book cases, is fully carpeted, has heavy curtains and as a result it is sonically 'dead' and is a much better place to listen to music.
Sorry this probably doesn't help, but really there is no getting around actually listening to the speakers or reading a lot of reviews and looking at the specs if that is not possible.
If speakers packages sound bright, it will be because of the speakers characteristics and/or the room, not because of some mysterious mis-match with the receiver.