You shouldn't need to resort to Search&Replace to make it work. It's not immediately obvious to me why your current settings aren't working. Difficult to say more without trying it myself.
However, I would be tempted to do a minor edit to the raw html file before you import it to Calibre. Try changing the <body ...> tag by removing the red bit
<body bgcolor="#ffffff" style="FONT-WEIGHT:normal; FONT-SIZE:small; MARGIN-BOTTOM:245px; LINE-HEIGHT:normal; FONT-FAMILY:GeorgiaEInk15" text="#000000">
Then reconvert with your existing ExtraCSS.
In fact, most of the info in the html's existing <body ...> tag is redundant. You could try simplifying it right down to
and see how that converts.
Edit: If none of that works I can only think that the font filenames are not quite correct. They should be stored in the reader's internal memory in a directory [drive:]\fonts
and the filenames, Amasis-MT-Bold.ttf
etc., must match exactly those in the @font-faces. All filenames, directory names are case-sensitive
The only other thing to check is that the Amasis font files are stored in the reader's internal memory in a directory called