I also fly the 717, and I’ve spent the last year attempting the find a solution to this very same thing. Here’s what I’ve discovered...
First of all, the Telex Airman-8 is NOT compatible with the 717. I know this from personal experience and have since read numerous online reviews stating the same. The Airman-8 seems to be unable to filter out the electrical noise that the 717’s lighting rheostats create resulting in a constant, unbearable tone.
The Telex Airman-850 works well on the 717 and by rotating the earpieces 90-degrees, it folds almost flat making it easy to find a place for it in your bag. Sound quality, however, is only slightly better than the Airman-750.
My favorite headset, and the one I am now using on the 717 is the David Clark DC Pro Passive. ($365 new) This is virtually the same headset as the DC Pro-X ANR, but does not have ANR making it half the price. It’s comfortable, well built and passively blocks quite a bit of noise on the relatively quiet 717. Most importantly, however, is that the sound quality is the best I’ve experienced from any headset. I can actually hear and understand ATC with such clarity that I don’t have to crank up the volume. It folds up nicely, however it does take up a bit more room than the Telexes.
That’s my two-cents. I hope it helps!