Lo Z was the way to go.
Your friend might try Amperex 6922 USA white label, or Siemens 6922 (E88CC). These have far more clarity and balance than the Brimar, which are known to sound fuzzy.
The Philips you tried might have been made by Amperex, but in my experience Philips tubes have always sounded less refined than Amperex tubes even though theoretically the Philips tubes could be of similar construction.
Anyway, just a suggestion.