https://www.youtube.com/watch?v=Qrs0oa-XIV4
https://www.youtube.com/watch?v=Hlcvgrk8H8g
I've always like the sound of V6 engines over V8's !
To me, it sound quite good! Better than a 996!
The subaru flat 6 is big and heavy, and not that powerful.
Also, it's probably harder to source.
The Audi v8 is a good option, but the engine costs a lot too. And it might be a direct fit on to the gearbox, it's not that easy to fit in the boxster.