Power Cord for Accuphase Amplifier

I have a new Accuphase P-4600 amplifier and am looking for a power cord to replace the stock. So far I’ve tried the Cullen Crossfire and the IceAge OFC Frankencable. While both cables have worked well on my source components they have not performed better than the stock on the amplifier. So to those who have Accuphase amplifiers what power cable has worked for you?
 

As I mentioned in other threads Accuphase strongly recommends that you use only the stock cord and so far that has been the best. The. other two have resulted in a darker sound with less soundscape openness. 
 

I’ve been trying to stay under $500 for the cord but would be willing to go a little higher if it improves the amps performance.