So you are looking at $6k to get 8 audio zone outputs up again?!? You've just convinced me NOT to recommend ReQuest's F3 and movie players for a long term and valued client. Totally unacceptable that they are taking no responsibility for a supply chain that they should have recognized as limited. They should have ensured they had contigency stock for the viable life of the product. They are not alone in this: the mighty Crestron dropped a huge brick with thier TPMC-10 when the batteries became 'unavailable'. 'Yeah ...... just toss your $4000 tp out ...... we've got something better now.'
Taking a practical view: is it feasible to replace the IQ touchpanels? The servers are very versatile (IP, IR 232) so control from an iPad with suitable app (RTI?) could be an option? Your client ends up with a versatile control system no longer locked into IQ hardware. As you didn't sell them this system directly I guess you need to present this as an opportunity to 'rescue' thier installation.