Seeking horn array loudspeakers with a maximum price of $17,500.00 per pair.

Look at Joseph Crowe Audio. 

Most of my listening is at those volume levels and the sound is rich and full.

my amps are 4.5 watt monoblocks type 45 tubes.

Another Volti recommendation. But if I were you, I'd be looking at high quality SET amps to replace that Brightson......

 You have some great choices at your price point, especially if you consider used.

Agree with ozzy62, I would not want your amp with horns.

Agree with @vicdior . The Fleetwood Deville. Did an audition recently. They are difficult to beat at that price point. Definitely something to go listen to. Some don't like their look however. Best of luck and keep us posted.

If I were in your shoes with that budget, my choice would be to take that dough and get a nice pair of custom veneer Volti Lucera's or a used pair of Rival's then spend the remainder on tube amplification. I had the Rogue RP-1 and liked it very much. Paired with something from Cary, or Quicksliver would be pretty awesome. I have yet to hear a loudspeaker that knocks dynamics, tonal quality, and midrange out of the park like Volti's do. IMO of course.