Power cables do make a difference, If you haven't heard it you either aren't listening or didn't try the right one. You will have to solder the connection to the amp board and a large diameter power cable will require you to probably drill out the case and find the right grommet. The GR is good because you can specify only one end but getting the other to match up is going to take some work.
For my Dynaco amp I used an inexpensive heavier gauge power cord because getting really large wires or cutting the case to put a plug adapter was more than I was prepared to do.