I have quite a few cans personally, but I feel 4 cans fill my ultimate needs. I'll break down my logic:
2 cans for home:
HD650: laid back, "fun" pair. For super long listening sessions. A bottle of cabernet/scotch and a comfortable chair. Sit back and zone out. Wake up in the middle of the night and realize you are not in your bed cans.
Beyerdynamic DT990 Pro: analytical pair. For when you want to be an active listener. When sitting back ain't enough. When you want to hear the things you never heard before in a recording. For when you want listen for the scratch of a pick. When you want to hear the break in a voice.
1 for the gym:
Sennheiser CX500B: highly underrated b/c of all the fakes. Great with my cowon z2. Good jogging, mountain biking, skiing, et. al. Much smoother, laid back, and fun than the Klipsch S4. I hated the S4s.
1 sealed pair for the road:
AKG K550: great sealed cans with amazing soundstage. Awesome for plane rides. A bit bulky, but packs away safely in my UDG case. Great neutral pair for home, as well.
So for me, 4 is enough. Most of my future purchases will be towards replacing the holy quadrology. I may add a 5th, aka a rock-oriented pair or a planar pair like the HE-6/HE-500. But 4 is enough. 5th pair is just vanity. I'm not a huge headphone roller like many on head-fi. Once I love something, I hold onto it for a LONG time. I'm not looking around the corner for upgrades. I've had my mdr-v6 forever. I only replaced them finally when a closed can with great soundstage entered the market, the K550s. And i won't be selling the MDRV6s with Pearstones...too much nostalgia. And I'll pop them in every once in a while just to see why I loved them so much.
I am curious how many is enough for you? What brand/model do you keep, and why? Is it vanity? pack-rat? are you a collector? or b/c they fill a void in your listening habits?
Edited by Eargasmo - 9/7/12 at 11:00am