When I look at the picture of the R2R relay-based volume control, I don't see as many relays as I would expect. This leads me to a couple of questions:
1.) Is the volume control balanced or single ended?
2.) How many volume steps are there and what's the step level?
It will probably be unbalanced like most headphone amps and preamps with relay based volume control. Even for only 64 levels, there would have to be more relays.
This is also the case with SMSL SH-9, SP400, Sabaj A10h and A20h.
Of course, it saves a lot of components and circuitry, but above all space. Since it is handled in exactly the same way with many devices of the "high-end" classes...
For modifications and repairs, I use the inexpensive 22-stage pots with SMD resistors as replacement pots. These 22 steps have never been a problem before. If a person turns a volume knob in the smallest possible steps to the end, you end up with 30 - 35 steps. The old Alps potentiometers with detent had 41 stages.
Under normal conditions, more than 64 levels are just a waste, also through experience with 128 and 256 level modules (which are also available in symmetrical versions).