What Instrument would you listen to?

My own. :)

I actually do often audition equipment with horn music, sometimes with recordings of my orchestra.

But to give a more serious answer to your question, the human voice would be the one to use, and not just sung, but also spoken. The horn is not a bad second choice, though, as it has one of the more pure timbres, acoustically speaking, among the orchestral instruments.

Some folks recommend piano because it is a difficult timbre to duplicate. If you want to try another very complex tone acoustically, than the oboe is a good choice. But if the more pure timbres are not resolved very well, then certainly the more complex ones won't be, so I would first use instruments with less complex timbres.

Almarg, they are out of print. Looks like they are going used for ~ $80-200.00. It also looks like some of his recordings are being reissued. I will keep an eye open for reissues.

Piano it is. Thanks for playing ball with me

I remember the sales guys in the shops being proud of certain speakers capable of reproducing piano exceptionally well. It's not an attribute one would have to discover on their own. So I think a well informed individual would by necessity choose piano firstly.