Seems like 'system' can be anything.. iphone and the stock buds are technically a system... and I use that when biking. I'm looking at wind-stopping solutions for that system now.
I think the spirit of the post was sort of a 'how obsessed are you?' kind of thread where we discuss how we have 2 or 3 systems as our tone controls in 1 room; kind of an obsessive hobbyist mindset.
If I'm just bragging about my systems, because I like them:
1- Main rig in basement; hasn't changed much in years... tried a few things but just upgraded what I had in the end.
2- Middle-floor audio; bookshelves, integrated amp, background and fun music.
2a - B-channel's go to deck speakers for seamless entertaining with consistent experience musically.
3- Upstairs bonus room in-wall HT 5.1 setup w/ streaming driven by receiver
4- Master bed and bath luxury system; driven by A/B channels from receiver using SB3. Synchronized music for whole-house experience.
5- Headphone setup 1 - ADL 128+ADL amp w/ my phone
5a - Headphone setup 2 - Sennheiser Momentums
5b - Headphone setup 3 - Bose earbuds, iphone buds, etc. for biking
6- OEM car systems (1 per car)
So are 5+ systems 'enough'? I think so.