Actually the above list is quite comprehensive, I couldn't have said it better myself.
- Try to talk to the team members directly and see if they have a different story to tell. It might be that the solution architect is skewing the facts a bit.
- I am assuming that your Project Sponsor is your Program Manager - if different you will need to inform your project sponsor as well of the situation
- Make sure to get a detailed report from the solution architect and the create a digestible, easy-to-read report out of that report and send it to your project sponsor (that's before assessing the impact on the cost, schedule, and scope)
- Offer alternative solutions to address the problem, and each solution should be accompanied with a complete study on its impact on the scope, cost, and schedule. The project sponsor and/or other stakeholders will be able to choose as solution.