Good to hear your impression of new KLH models. In reference to your two pair of restored original model fives, I've also restored my pair of originals, which sound better since new in 1973. The biggest performance enhancement was crossover network restoration in 2015. I followed a component design supplied by J Kent. I recall using highest grade caps and resistors available. I didn't skimp, money wise, which has paid sound dividends ever since.
I next added less impressive improvements from refinishing cabinets to resealing cloth surrounds using RoyC sealant applied as needed to woofer and midrange. I replaced original frame gasket material with a tight sealing black tacky-backed material. In order to make cabinets as air tight as possible, I sealed midrange enclosure wire holes with plumbers' putty to eliminate passive, out of phase, movement on midrange drivers. Woofers now act normal, and are slow to return to center. Base sound range is consistent, lively, agile, without boom. Also, much credit for sound quality is a 15 year old McIntosh tube preamp and SS amp.
Apple Mac mini M1 controls the system, including preamp and amp. The streamer source is Apple Music. Mac mini is latest version of macOS Ventura 13.3.1. Up to this point, no additional operating software, or hardware, is needed. The Mac mini/macOS provides a robust, abundant set of sound tools including a reasonably up-to-date DAC chip, basic EQ, and digital tools, such as sound correction and speaker placement. This is not a dedicated Mac mini, it also provides all the other normal functions of a personal computer. Latest 2023 Mac mini M2 is $499.99, for some, the best value in modern audio, digital or analog.
My listening room is small with eight foot ceiling and sound insulation (furniture pads from Harbor Freight) covering about 75% of wall space from ceiling to two feet above hard surface floor. Speaker placement and listening point is on a perfect triangle shape about 7 to 8 feet separating three corners. These 50 year old model fives are canted in at about 45ยบ on 4 legged stands at thirty inches tall. Cabinets rest vertically on stands at 58 inches. Left and right cabinets placed center of corners about 22 inches from center line of rear cabinet baffle. Sound alignment is centered to a seated listener.
This is a great hobby, always looking for perfection around the next corner.