Ditto the source and the power cords. Regarding power cords, I just replaced the stock power cord that came with my Musical Fidelity A5 integrated with a 1 meter PS Audio Power Punch ($49.95) and the improvement was SUBSTANTIAL; more bass and eveness of response. Mids are much better, more tube like and warm. What the heck is going on?
I was not a believer that power cords could make a difference. I was one of the world's biggest sceptics in this area, but this made such a huge improvement; even this modest expense was very noticeable and positive. One tweak that must be explored.