There are a couple of systems you could consider. One is a raised floor system - you only need about 6" for both air and data/electrical. The problem will be the demising wall requirements. The other is a small diameter, high velocity ducting system. It uses 2 - 4 inch ducts with a high speed air flow.
The previous message is correct, you need a mechanical consultant on board now to resolve these issues.
One other option is a split system approach. Systems by Sanyo and others use remote condensing units and small wall or ceiling mounted air handling units - these are ductless systems also. I've used them in remodel situations where there were not any options for ductwork.
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Jack Romigh AIA
Fort Worth TX
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