I have 3 amplifiers and 3 sets of speakers. All used in one system only at present and in rotation. If I don’t use something for a length of time, say 6 months, I will likely sell it. Reasons are I don’t like clutter and I believe it is better someone else can enjoy it rather than it gathering dust in a dark corner.
How long do you keep Hifi you don’t use?
Lol measured in years not months. Some measured in decades. 
Years, I usually try not to keep additional or surplus amps and speakers dormant for more than 5 years. Four amps, two pairs of speakers. Ideally not more than two years.
This
Seconded!
Don’t get it. Why keep something for a long time when not using it? Is it about hording belongings? Can’t you let go of it for some reason?
Yes, and obviously!
I have plenty of space and I don’t think about it much. So my actual and psychic holding costs are zero.
In my case, not hoarding at all. Some of the items (amplifier and cd player) in storage are not mine. They are owned by Mrs E of E. I have one CD player in storage, which is for backup to be able to play CDs directly if/when the Naim UnitiServe finally fails.
I have a range of loudspeaker cables of various lengths, which (if you follow my main thread) you will understand are periodically brought into use depending what is happening.
Decades!
Decades. My A60 hasn’t been used in almost 25 years.
I have to actually dislike something to get rid of it.
Lately I have been more into gaming so the big Naim system has been powered down for 8 months. Totally normal. No need to get cold feet.
I don’t have any hifi that I don’t use, and I never have done ever since getting my first Naim in 1983.
Having one system but rotating three amplifiers and three sets of speakers would confuse me.
Never had multiples for more than one week.
Same here. I still have my pair of Spendor A9’s from when i bought the pair of Sopra N2’s a couple of years ago. I probably never will get round to putting them in an AV system lol.
Currently have had Dynaudio Contour speakers and cables for about 15 years. Also have had spare Chorq Qutest DAC for over a year. Once I get my main system back from dealer, the NT50 will be added to make a second system for my office (where I occasionally do the boring admin stuff). Slowly slowly build up a second system.
My garage is full of stuff I have kept for years “just in case”! Musically, I still have Sony TC-K611S tape deck which has not worked for years and I have been meaning to repair (replace the belts).
A good friend of mine bought a classic car in pieces, including a lovingly refurbed engine. Knowing him well I said at the time to not buy it but to look for a finished example even if it costs more.
Of course he did not listen 
. 7 years later the thing is still in pieces in a lock up.
It was actually slightly worse … before he bought the above he obtained the same model, also in pieces, but looking like a swiss cheese, full of rust holes. We couldn’t believe it. Stoic as he is it was ‘no problem, I know someone that can fix this’. A year later he moved it on, nothing done on it and amazingly enough did not loose too much money.
I still have my Rega P8, which actually hasn’t been used for over a year since we moved houses; does that count, or is this a different topic? 
I never keep any hi-fi that we’re not using. I’ve never had the slightest interest in swapping components around in a system. I just choose what sounds best to me and use that. I dislike even having more than one source at any one time. One will almost certainly be preferred over the other and to me that makes the preferred one the only sensible thing to listen to and the other one totally redundant. Likewise with swapping say speakers or amp, almost certainly one will be preferred over the other so why waste valuable listening time with the less good one? This sort of thing to me smacks of more interest in equipment than in music.
I have not used the Aro on a regular basis in more than ten years, but I have not sold it.
But now it is installed in a early 90s LP12.
It is a beautiful piece of kit and I do not need the money, so I will keep it.
I also have some other Naim kit somewhere, a CB HC, 62, modified Snaps and SL2.
There are several reasons. Firstly there is no urge to sell as I can afford to keep. Secondly all the surplus amps and speakers still appeal to me and all sound great. There are no bad sounding amp/speakers. Third, I like to swap amps and speakers once in a while for fun as sometimes I get bored with the sound and wish to experience something different. Somehow I think having multiple amps prevent me from considering another new upgrade.
Lastly, I don’t really like selling stuff, the hassle of selling. Nevertheless, that will eventually happen sometime in the future but not at the moment. I just hope I don’t add more clutter to the current collection.