That Junior Financial Engineer position looks exciting to me!
I think I'd qualify for the Sr. one, in terms of C/C++, the math, and the Linux experience, but I'd never held a "financial" job before. Having to move back to Boston wouldn't be ideal but I lived in Cambridge for 7 years and could do it again.
I also really dig lots of the topics I see on the company blog, and will be reading them later. Are the compensation numbers I see on glassdoor in the ballpark?