The bottom line is that the Rx MK3-B is one portable amp that sounds much bigger than it looks; it’s a pocket-sized powerhouse that can belt out music with serious gusto.
What’s the benefit of multiple gain settings? As mentioned above, the Rx MK3-B’s three gain-level settings allow users to match the amplifier's gain levels to fit the sensitivity of their chosen earphones or headphones. I found the best approach was to experiment by ear and then to choose the lowest gain settings that would still allow adequate volume levels with the earphones or headphones at hand—an approach that gives the best overall combination of low noise levels with satisfying volume levels. In practice, this meant I used the amp’s “Low” gain setting almost exclusively for high-sensitivity in-ear monitors, the “Medium” gain setting for the majority of listening scenarios, and the “High” gain setting in those instances where I needed/wanted to drive ultra-power-hungry headphones.
What about noise levels? I found the Rx MK3-B was absolutely quiet enough to use with high-sensitivity in-ear monitors, provided I first engaged the lowest of the amp’s three available gain settings. With the gain switch in the “Low” position, the ALO produced no discernible hiss or hum when used with either my Westone Elite Series ES5 custom-fit in-ear monitors or my Ultimate Ears Personal Reference Monitors. Indeed, the Rx MK3-B gave better results with the Westone monitors than other portable I’ve yet heard.
Interestingly, the Ray Samuels SR-71B might be just a smidgeon quitter than the Rx MK3-B, largely because the SR-71B offers slightly lower gain settings (and thus potentially lower perceived noise floors) than the ALO. Even so, I felt noise differences between the amps were so subtle that I doubt most listeners would even notice them.
Got Power? With its balanced outputs brought into play, the Rx MK3-B had sufficient power to drive even the brutally demanding HiFiMAN HE-6 headphones, although my sense was that the HE-6 pretty much used up every ounce of power output the ALO amp had to give. For all other headphones, though, I found the ALO amp had more than ample power, typically serving up expressive and, where appropriate, explosive dynamics.
Compared to the Ray Samuels SR-71B, the ALO Rx ML3-B seems at first to be the more powerful amp, although in theory the SR-71B offers somewhat more power output because it features higher voltage battery packs than the ALO does. What tips the balance in the ALO’s favor is the fact that its higher available gain settings help users tap the power at hand, whereas the SR-71B sometimes begs to be run with its volume control wide open.