Simon,
I tried the GZ37. It was even mushier and muddier than the Mullard GZ34/5AR4. It was a total waste money, IMHO. The overall dynamics were very weak compared to the 6106.
In my system, the 6106 adds much cleaner and more immediate dynamics with a much more palpable 3D presentation than either the GZ34 or the GZ37. No comparison in the soundstage. YMMV
I tried the GZ37. It was even mushier and muddier than the Mullard GZ34/5AR4. It was a total waste money, IMHO. The overall dynamics were very weak compared to the 6106.
In my system, the 6106 adds much cleaner and more immediate dynamics with a much more palpable 3D presentation than either the GZ34 or the GZ37. No comparison in the soundstage. YMMV