I understand the situation and the events that lead to this.
Customers very rarely understand what they are doing. For some unknown reason in this current society, most everyone do seem to think they know what they're doing when it comes to electronics. I can't explain it, these same people won't take the engine in thier car apart to fix it, won't put a new roof on their house themselves, won't defend themselves in court without a lawyer, won't do surgery on themselves, but hook up a complicated whole house A/V system.... no problem :lol:
A couple of things that might help you in the future:
1) The customer is NEVER to dictate what equipment is installed. If they have a shopping list of stuff they bought, best to leave them to themselves. You already have an example you're dealing with as to why. Many more reasons than that however. If (big if), 'all' the equipment is stuff you are already familiar with and use; then you could make the decision to do the work. But it should only be done as T&M (Time and Materials).
2) Own the job. You will get blamed and expected to support anything you touch. If there is something already installed that could cause problems with the system you're doing, give the customer a price and replace it - other wise you can't warranty the 'system'.
3) Know what your doing. This should seem like common sense but when work is slow, companies seem to try and do all kind of things they shouldn't. It kind of sounds like this was one of those cases. You need training and experience on anything you try to do in life. If there is a job that is paying for a professional and it's outside of what you know, you need to either pass it on to someone else. Or get the training and support from somewhere to tackle it, then you can go from there.
[edit]: forgot to add. If you drop the system down to 480p, disable all HDMI CEC stuff (control), and disable bitstreaming on audio (PCM only). You should get video to work over the 100ft runs.