sperandeo - I use my LCD-2 far more than I use the Stax rig, or various reasons.
1) When I'm not thinking about it and just casually grab a headphone off my headphone stand to watch a movie, play a game, or listen to music, I grab the LCD-2 because it's more satisfying than the HD650 overall, and it doesn't require me to have to turn on an additional amp like the Stax does.
2) When I'm using headphones to do critical audio work, I alternate between the LCD-2 and the HD650. The LCD-2 is used to make sure the overall balance and bass frequencies are mixed properly, and the HD650 is used to make sure the mids are okay. The Stax is only used in this context as a third opinion, to make sure that my mix sounds good on any headphone or speaker, but I could easily use any other headphone for additional opinion. I use the Stax because it's on the headphone stand and all my other headphones I've put away in the closet until I need them for specific tasks like tracking.
3) When I'm using headphones for more focused leisure listening sessions, then it's a toss up between the Stax and the LCD-2.
4) If I ever need to sell something due to money problems, the Stax will be the first to go. The LCD-2 I'll never sell, unless things get really, really bad and too much as at stake. The M50 I'll never sell (because I need at least one pair of closed headphones for tracking), and it's worth almost nothing anyway. I would sell anything else in my collection without caring too much about it. But the reality is, if by the time you are near middle-age and you still can't manage your finances properly and need to sell off stuff to make ends meet, then you've got a lot more serious problems than deciding which headphones to sell/keep.
5) I really don't use the Stax rig all that much--maybe 10% of the time. The LCD-2 about 70% of the time. The HD650 about 20% of the time. The M50 only comes out when I need to do tracking. The W3 only when I go out with the mp3 player. The others I pretty much never use.
Would I use the Stax rig more if it didn't involve an extra amp to turn on or off? Probably. Seems trivial--that dealing with an extra amp would be an issue, but because the LCD-2 already sounds so good, I really couldn't be bothered to make that extra effort. The only time when I feel like I really want to turn the Stax rig on is when I'm in a particular mood where I want to hear the special presentation of the Stax rig. So basically the Stax rig is an luxury item that's rarely use in daily life. Sort of like if you had more than one car. The LCD-2 is like a practical but very high quality everyday car, and the Stax is like that exotic sports car that you rarely drive and keep in the garage most of the time.