The "complicated stuff", including the vinyl-spinning side of things, isn't touched by anyone but me. Having two humongous extreme isolation transformers and three mysterious big black boxes and two toroidal isolation boxes feeding into a row of separate power supply units (including the Magnum Opus one Power supplies, with their glowing tubes behind prison-bar-like cages), plus a few units and controls not found on a lot of "regular" stereos that non-audiophile people are usually familiar with (most people don't understand "gain", "bias", etc...), makes the system look a little intimidating. I think a lot of people wouldn't dare mess with it, anyway, because (unless they were familiar with hi-fi stuff) they wouldn't know what to push.
My wife complained for a while about how complex the stereo was (like the comment above about needing all those knobs just to hear the news), and would just sort of randomly push buttons and turn knobs "until it worked"
I had a few scary moments result from that, and she had some frustrating moments, so setting up a simpler system for her only, was the best solution for both of us. With "his and her" systems, peace of mind and peace itself reigns. She listens a lot to music from her laptop, using earphones, anyway.
But I don't EVER leave strangers (or even friends) alone in my home, anyway, so there is little-to-no chance of an outsider working the system. Either I or my wife will be home, if anyone else is here. I've made rare exceptions for visiting immediate family members, but that happens about once in a decade. My older brother would know how to work a stereo, and I'd trust him (he used to own a company that made conformal coatings for circuit boards; he understands electronics well enough!). My other relatives know how I feel about my stereo gear, and probably wouldn't touch it, anyway. And no one else would have a chance to get near it, without my presence. If my wife wanted music for visiting friends, she'd use her system. No problems.
But would I trust someone in a situation like the OPs? Not entirely, not most of the time.
I'd take any gear I really cared about and make it safe, either by locking it in a closet or removing the fuses, etc... Then I'd set up a simpler system with gear I cared less about, so they could still have music when they wanted, and if they screwed it up and damaged something, the loss wouldn't be catastrophic. Probably a mid-powered receiver with input cable set up so they could connect their laptop, and an iPod dock, perhaps a CD player. Decent but expendable speakers. If you haven't hoard- er, collected enough gear to do this, then simply remove the TT (which is the most fragile part, that they are most likely to screw up/damage) and make it easy for them to connect an iPod, as suggested. Give clear instructions, and explain that the stereo is "your baby" and you're nervous about anyone else playing with it (let them think you're weird... at least your gear will be safer.)
If I WERE to let someone use my system, as-is, I would do a few things. First, I'd write out clear, step-by-step instructions. A user's manual, so to speak, so that as long as they follow the instructions carefully and don't "get creative", there won't be any problems. I might put color-coded stickers beside knobs that match the instructions, to make it even more idiot-proof. I might also explain to them the rarity of some of the gear I have, and how I view my ownership of these units as a caretaker's responsibility, a bit like a museum curator's job. If they choose to use the stuff, they should assume the same role of responsible caretaker. If they can't understand that mentality, then perhaps they shouldn't use the system.
All that said, I wish I were more like people who DO trust others more with stuff. I remember when I was a 15-year-old with a learner's permit. A man let me drive his car through the Snake River Canyon (one of the most treacherous paved roads in North America) in one of the worst storms I've ever been in (visibility often didn't extend to the road surface; I drove much of the way by keeping the bright taillights of the truck in front of me equidistant!). I was shocked that he trusted me that much; he was in the car, too, and both our lives and that of his son were at stake... but I was also grateful for that trust. That experience gave me an increased level of confidence, and after word of it got out, I was given a job shuttling cars at a summer camp, which gave me a chance to drive a variety of vehicles. For a kid, that was cool! I've never forgotten that trust, and other examples like it. I'm still grateful to that man, and respect him for what he did.
I think it is a good thing to be able to show trust in people, at least sometimes. Sometimes it builds them up, and shows that you respect them. Trusting people more (rather than less) is often good Karma, so I try to do it more and more often... but there are practical compromises, too. You have to think of (1) who the person is; (2) what gear is involved; (3) the likelihood of mishap; and (4) whether you can accept the worst-case scenario (=broken gear). Sometimes perhaps broken gear would be a small price to pay just for the chance to show trust in another person. If your sister wouldn't understand your reluctance to let her use your gear, and would hold it against you if you didn't let her use it, then the risk of damage might be less important than the certainty of damaging your relationship. Let the answer suit the circumstances.
