You can send your hypotheses in your email. Bottom line up front, getting to the point as fast as possible avoiding the caricatural grandiose startup diatribe of how your company will change the world, or what has lead you to start it to fulfill a childhood dream.. It is much easier to receive a reply to an email containing something to disagree with, than it is to an email asking to set a meeting.
If you have a prototype, you can open an account for them, send credentials, tell them what it does, and ask them what they think. You can also send a screencast.
In my experience, being candid, jealous of and careful with people's time made them more generous with their time.
Something like that. Ask specific questions if you want answers. Make it easy for them to write a one- or two-sentence reply and you'll get paragraphs of valuable information back.