Power Cord Question

Darkeyes, for what its worth, you'll get the biggest bang for your buck with a good powercord, even more so than going to the next component upgrade.
I would recommend you trying the fusion line. Their entry level cord is the predator($550 retail)but you can get it for around $300-$350.
Go to their website www.audiosurroundings.com. The contact person is Eric Love, a very good person to deal with.
He will let you demo his cords, if you don't like you can send back and get your money. The only downside is it takes 150-200 hrs. to break-in.

A lot British companies make components with two prong iec connectors. They work perfectly fine with 3 prong powercords.
I had a arcam cd player made that way and played it for 6yrs. without any problems. If your house is properly wired, all of your outlets are grounded from the main box which makes it safe.

I've tried some of the same powercords you have tried and yes you do have to let them breakin, at least 100 hrs.
The BMC gold powercord was a definite improvement over stock powercords in my system but to really appreciate what powercords can do, you're going to have to go to one that is considerably more than what you're currently trying($600 would be just a little past the starting point)
I've been in highend audio for over 25 yrs. and if you had told me 15 yrs. ago powercords would make the difference/improvement that they do, I would've told you that you're crazy!! But when you hear the higher tier shunyata's, purist audio, fusion cords and others, then you'll know, they can make a huge improvement in your system
and on your power conditioner.
In your system however it may not make good sense or be cost effective.
In other words, would it make sense to put $1000 powercord on a $600 amp? I don't know probably not.
Just my two cents worth.