I'm understandig this AMHash thing that way:
AM is selling tubes/prismas in bulk with a little lower price than 1.0BTC/TH to RM. With delayed payment agreement.
RM is building a farm (adding PSU, infrastructure etc.) and selling shares of that farm (1.25BTC/TH). When IPO will close RM will pay for hardware to AM. If not all shares will be sold RM will mine for AM, taking maintenance fee (or AM will be the owner of shares). Deducted from previous answers of rockxie.