I can relate, if you have a nice piano you want it to sound nice 
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My setup is a bit complex but most important: I have a Mackie ONYX 1620i which is a 16-channel analog mixer with 16in-2out firewire audio interface built in. It allows me to route any input to Cubase, but every input also goes into the mixer so I can create a monitor mix without touching Cubase.
The powerplay is a 4channel headphone amplifier which I use when recording multiple musicians. Great value for money and some clever features. Doesn’t sound great but as I said, it’s only for recording so that matters less.
Converting mono to stereo is unfortunately not possible. When the UR22 sums the left and right channel together there’s no way to separate them again. Yes, there are devices that can ‘make up’ stereo information from a mono source to create a stereo effect but it’ll never be the same as the original signal. The product you posted doesn’t seem to do that, it’s a headphone amp with a 2 channel mixer which is clever in its own right, but not exactly what you’re after. It might be cheap but not cheaper than an extension cable for your headphones 