1. Xbtool only supports current BIOS releases. Since EvoX 2.5 is in the vicinity of 2 years old, it's not supported by any recent ver of Xbtool.
2. The bios.bin in C:\backup is 1MB probably because when EvoX 2.5 was flashed to your modchip/TSOP, the image was mirrored across 4 x 256K banks. The EvoX dashboard would have grabbed the entire 1MB block.
3. You don't have to mirror the 256K X2 BIOS to 1MB in size. Pretty much any fairly recent flashing utility will mirror it for you.