I have to say I have heard the akra in person at the track and it sounds really good.
that said, I like the metallic howl of the MPE and for me, its by far my favorite exhaust sound. it has a very unique sound, sort of like if you combined the s65 and s54 sounds together.
I think the MPE is the exhaust that sounds the least like the rest of the exhaust offerings out there. its up to your personal discretion whether that is a good or bad thing