Check out Moondance Audio @ 1881 S. Broadway
(303-777-4449; closed Sundany & Mondays). They are going out of business and everything is drastically reduced; including their JM Lab, Martin Logan and Usher speakers. I've been dealing with them for years and will certainly miss their honesty and integrity.
Sorry to hear that Moondance is going out of business. I've purchased a fair amount of equipment from them over the years. (I relocated to the New Orleans area earlier this year.) In addtion to Audio Unlimited, you can try Denver Audio Designs, (Krell, VTL, Thiel, PSB, Arcam); Cherry Creeek Audio (Audio Research, Krell, Revel, Magnepan, Vandersteen). There is also a shop on Belleview in the Denver Tech center whose name escapes me, but they carry BAT, Jeff Rowland, Vienna Acoustics. Another option is Listen Up. They are mainly geared to HT, but they do have B&W, Sonus Faber, Musical Fidelity, Rotel, Classe. Finally, I'd schedule a visit to see Jim at Sounds Real Audio. If I'm not mistaken, I think he sells only tubes. Last visit there, he had DeHavilland, Sophia Electric, FJ Loudspeakers, Wilson Benesch, Cain &Cain. There are also great stores in Fort Collins and Colorado Springs if you have time to get there. FWIW, I've lived in 6 different metroplitan areas, and I think Denver is hard to beat for Hi-end audio. Hope this helps. Good luck!
I'd also recommend Jim at SoundsRealAudio.com, check his website for his product line and also call to see what he has in stock. He sells and demos systems from his home and I've found him to be very helpful and a nice guy. I think he matches components well for his demo systems, I especially liked his Wilson Benesch/Dehavilland/AA Capitole system that I listened to at his place.