Hi, I'm Matt and am looking to help you (22 years of IT development).
Thanks for sharing a link to Presentain. What you need is a (web) system that automatically refreshes clients (slides, if checked to advance with a presenter), offers good security and is relatively easy to maintain.
So I assume you are using ppt2npng and pdf-image (node) modules. These would most likely stay.
My bid is to use Meteor (a node.js framework) application for client updates (automatic slide changes), security (logins with social networks if needed) and integrating all. The work would include:
1. Draft application - converting, displaying, syncing slides (on client browsers). Adding skeleton code for future enhancements (polls, questions etc).
2. Authentication added - internal logins and social network profiles (all stored in a database).
3. Some enhancements like reporting number of users who watched the presentations, requests for additional information (file, contact etc), iframes for future additions (for live PIP of a presenter etc).
This bid therefore does not include a mobile app development though viewing the presentations on a mobile devices (responsive design) is included. You are welcome to disscuss more since your requirements like simple USB connecting and automatically converting and starting a presentation preview are way beyond simple app development.
Looking forward to your reply (otherwise am PowerPoint guru from 1994 and was system engineer for 6 years),
Matt