What other hobby...

What do you mean by an "infinite number of variables"?
Are you referring for instance to all the factors involved in choosing "what is the best [X]?" (where "X" = speaker/amp/cable etc)?
So for example in choosing speakers, one might want to consider price, size/weight, build quality, local availability, placement constraints, Wife Acceptance Factor, etc etc, not to mention factors of SQ such as frequency response, dynamic range, bass impact.

Now try framing a similar question for another hobby.  Say, woodworking. What's the best workshop set-up and choice of tools for a budget of $N? You'd be facing a whole 'nother complex set of variables and supporting questions. Like, "Do you prefer hand tools or power tools?"  (~= classical or rock and roll).  

tk21, you and Douglas_Schroeder ain’t no fun. You both took a light hearted question way too seriously. I loved all of the answers except those from both of you. I fear you are both too contentious and defensive to ever be on my party list. 

Macrame

I got into antique jukeboxes around 1990. Buying, restoring, selling, collecting, etc.  I'd be up untill 3 am working on them.  I had nine at one point, I have three favorites now.  I joined the American Historical Jukebox Society.  Meetings, a newspaper, jukebox shows, jackets, the whole works. I met guys with so many jukeboxes they had no room for furniture. I still love those darn things I just don't put in that much effort these days. It was great fun, no regrets. 

I'm with oldheavymech in that I have a lot of gas still in the tank.  That said...
Downhill skiing.  I enjoy the art of tuning my skis and getting the most out of them.  Quick, sharp, and precise turns that secure the most g-force.

Offshore fishing.  It takes a lot of trial & error, and patience, to get those elusive bluefin tuna.  But when you do, especially the bigger ones at between 60 to 150 lb., what a thrill and what a reward.  All other pelagic species are a great catch too, but those bluefin tuna are the best thrill of them all.