Tom, Can't supply documentation about the 'U67 sounds the same as U87' idea. I can only quote my distinct memory of Russ Hamm (then an employee and later owner of Gotham Audio, former import of Neumann) telling me this. He also wrote the seminal article entitled something like 'Tubes vs. transistors: Is THere A Difference?' that was presented at an AES convention in the early 70's.
Not to get to Rodney Kingish, but can't the HLO and HLS factions work together? They can't live without each. THe HLO needs the HLS to know what he's shooting for, and the HLS needs the HLO to supply the science to achieve it. It's when these parties regard each other with distrust and suspicion that the arguments begin and progress stops. This situation probably arises because they don't understand each other: very likely, their different mindsets keep them from coming to common ground.
The best examples of the happy medium I can think of are Russ Hamm (an engineer with great musical sensitivity) and Bill Putnam. Within these two giants resides and resided the spirit of both the HLO and HLS. We need more like them.