What is they best album out there for showing off the sound quality of your system.

Doug MacLeod There's a Time

The Harmonia Mundi France recordings of Gregorio Paniagua and his Atrium Musicae de Madrid.  Anything on Todd Garfinkle's M.A. Recordings label.  Yeah, even the CD's have gangbuster fidelity.

After decades in this hobby, my experience has been that people respond most favorably listening to music they like, even more so if I have an album they like that also is well-recorded. 
I rate all my albums on sound quality, classes A, B, C and D. Categorically, the percentages are roughly: 10% class A, 50% class B, 35% class C and 5% class D.
So...I will play a class A or B-rated album in the genre that the guest prefers. Really rewarding to see their reaction for hearing recorded music better than they've ever heard it before. Priceless.

Sona Jobarteh ‎– Fasiya
the music, the vocals, the sound stage, and the quality of this album just blows me away every time I play it.https://www.youtube.com/watch?v=XlvBHMoPO34Another fave is The Be Good Tanyas - Chinatown https://www.youtube.com/watch?v=iNiHHZOY45Y

Flim & the BB’s - Tricycle
Mannheim Steamroller - Fresh Aire 7
Diana Krall - Live in Paris
James Taylor - Hourglass