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Sitting on my desk, connected directly to the Mini via the headphone jack, are a pair of M-Audio AV 40 speakers.

I also use a set of Grado Labs SR60 headphones, plugged into the headphone jack on one of the M-Audio speakers.

I also use a pair of Vandersteen Model 2 speakers, driven by a Denon receiver, via an Airport express connected via WiFi to the Mini, in my home office.

I also have a variety of WiFi connected devices around the house: 2 HomePods, a Grace Digital Encore internet radio, and a Sherwood receiver connected over WiFi with a Muzo Cobblestone driving a pair of very old Advent bookshelf speakers. Giving me pretty much whole house audio coverage sourced from the Mini.
 
~20 year old Bose Mediamate 2.0 speaker set - my only active Mini is predominately a headless server so I don't really care what's plugged into it.
 
I use the Bose Companion 20. They are nice and compact, I like the amount of bass and the control pod is great.
 
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