Word for someone that will take any challenge thrown at him, prepared to take up any challenge. Preferably with "omni" as prefix. Doesn't have to be word that is commonly used. I have been trying to figure it out for a while. Something like: "omni"-prefixed word for "all-hearing"
There doesn't seem to be such a word! 'Tis a pity, since it would seem to be useful.
However, such a word could be coined using the Latin word for prepared or ready: paratus:
Interestingly, Google Translate gives the Latin word parabo for "ready for anything". And omnes parati for "all prepared".
One could use "omnivorous" metaphorically to describe someone with an insatiable/indiscriminate appetite (for challenge, or indeed other things).