I know this is an old thread, but I have to say one thing... And I know that the original question was a grammar one... I swear I'll check my Elements of Style
when I get to school tomorrow, but....
I laughed so hard
when I read that Buddha "underwent severe conditioning"
I totally pictured him training for the Olympic bobsled team or something!!! I vote for Manuela's sentence, sorry.
Also, the original sentence's "suffered" and "awakening" are key terms in Buddhism so I think you could have kept them and just rearranged to make the sentence less awkward:
"He suffered in the mountains for six years in order to attain awakening."
Austerities has a good sound to it, but I don't know if austerities can be suffered. Endured, maybe?
OMG, I can't stop picturing Buddha in sweats!