Well, maybe i don't ask the question directly enough. As far as i know for Western Garmin devices there has not been an instance of the logo splash screen image contained in RGN/GCD firmware files, afaik certainly not in the ramloader aka "boot.bin" (which i'm assuming you meant by "boot.ini") or any other fw components meant to be flashed to other regions such as 14, 127, or 158 if populated. Those factory-loaded images which are displayed during starting are contained in rgn16 (hex 0x10). Some devices allow a change of splash screen image from within the device's setting menu but that doesn't change any other data in rgn16 which may be crucial to properly displaying the splash screen and if the device has been cross-flashed there is sometimes no way for the device to load from region 16 on boot-up. That results in display of a blank screen, sometimes with a small error message, rather than the usual splash image(s).

So have you tried with either HD 590 or zumo 595 or both to dump rgn16 with Ldr.bin and 'rrgn' text command and then examining the dump in GIR_Editor? It may be that the HD logo data still contained in rgn16 is incompatible with the zumo 595 firmware and so no image is displayed. Some conversions such as nuvi 37x0 to 34x0 also require a change of logo file, so that problem isn't without precedent.