I can't make a specific recommendation for your amp, but I do have a theory about your situation. As I've written before, I've come to believe - based on my own experiences trying different cords, plus logic and intuition - that while most components can have their performance improved in any number of ways and degrees by aftermarket PC's, they can still exhibit unwanted changes in perceived tonal balance at the same time.
My theory is that this phenomenon has a lot to do with the way components are voiced by their designers: *with the stock power cords fitted* (this is something I'm only presuming, but it makes sense). Therefore, the tonal balance is most likely to be as intended with the stock cord in place.
Replacing the stock cord with an aftermarket cord that is demonstrably 'better' in its design, materials, and construction will often improve many aspects of the sound, but can nevertheless result in unwanted tonal balance changes, simply because the component designer originally voiced the piece of gear to account for the cheap stock cord's intrinsic tonal character. So finding the best aftermarket cord for your component won't necessarily mean finding a cord that will leave *all* components' tonal balances unchanged for the worse - under my theory, such a 'neutral' cord doesn't exist - but will involve finding one which changes the sound in a way that you feel is the best combination with your particular piece of gear.
If I am in any way correct in my thinking, it will somewhat contradict Audioengr's perspective above. His view - certainly not incorrect as far as it goes - that a better cord will simply enable a component to more fully reveal its true response capabilities, doesn't take into account that the component may have been originally voiced to compensate for the stock cord's limitations, which to me could legitimately result in a sub-optimal tonal balance when those limitations are subsequently reduced or removed by upgrading the cord. And that's even if a lot else about the sound unquestionably improves.
So I think there's some reason to believe that even though there are undoubtedly 'better' and 'worse' ways to design and construct replacement PC's in theory, part of the result with any particular component will: #1) always be a crapshoot, #2) may have more to do with the stock cord's idiosyncracies than the replacement cord's, and #3) that this in large part accounts for why there can be a lot of debate over the relative merits of different PC's used in different peoples' systems.
I say this as someone who generally believes that any halfway-decent aftermarket PC worth its salt should at least do a better *overall* job than a typical stock cord, and I also acknowledge that there can still be be a lot of agreement about the 'sounds' of different aftermarket cord models. And of course as with anything else, everyone will also have their own individual preferences, and all systems will have plenty of other built-in biases which can change outcomes. Besides, this whole notion I'm talking about is hardly a novel concept when it comes to speaker cables or interconnects - but it is less likely that component designers will voice gear based on the way it sounds with just one kind of SC or IC, and even less likely that those wires will come packaged in the carton like a stock PC.
Furthermore, I can't discount the possibility that some cord designers deliberately aim to alter tonal balance with their products. Another factor going against my theory is that 'stock' cords are often rather a random item in actual practice, with different kinds being included dependent upon their availability or price. These generics may be similar enough on average to safely ignore the distinction, but if so, then my argument would still break down on the grounds that replacement cord manufacturers would then have a de facto 'standard' cord starting point to work from, and thus shouldn't be making products that diverge much from the stock cords' tonal balance. But, I'm not sure that cord manufacturers necessarily arrive at their designs with that caveat (or my theory) in mind.
I think about this idea every time I read where someone is claiming that XYZ power cord is indisputably 'better' than ABC power cord...what do you guys think? Am I wrong in assuming that component manufacturers aren't using aftermarket cords when voicing their components? Should they? If so, should they include such a good - and 'correct' - cord in the carton? And if that would be too expensive, is the current practice of hit-and-miss aftermarket cord upgrading satisfactory?