GrimShadow,
Lee is the expert here, which is why I decided to take a back seat once he got involved rather than hitting you with suggestions from all sides, but 'from the sidelines' I am starting to run out of options and as Lee can confirm I have had considerable recent experience tracking down weird boot issues which turned out to be due to a defective Pi rather than a PilotAware (PAW) issue, .....but you say you have tried more than one Pi2, so that should have eliminated a Pi hardware fault in your case.
Just to clarify the position, as I understand it, you have now tried the downloaded PilotAware (PAW) software in:
More than 1 different Raspberry Pi2s - without any attachments in any of the USB ports, and...
Using at least 2 different SD cards, both of which were pre-formatted using SD Formatter? with the format options set to 'Full Overwrite Format with Size Adjustment ON' before copying the software directly from the opened PAW software folder to the root of both SD cards.
...and you are still only getting the rainbow screen with the units attached to a monitor. Is this all correct?
If so, the common factors as I see it are:
Power Supply - are you certain it can supply 5v at 2 amps? Do you have an alternative you can try e.g. a 5v 2amp power pack?
Power Cable - this must be heavy enough to rule out voltage drop - can you try another cable?
Downloaded Software Image - What software version is it? Have you tried doing a completely fresh download in case the original has become corrupted? - I have had one occasion where this resolved a boot issue - so worth a try. Also worth trying another freshly re-formatted microSD card (you presumably have spares available), to eliminate the possibility of faulty cards.
Regards
Peter