The ARVA 3Axes was released in 09/2008 and discontinued in 09/2011.
Summary: The ARVA 3Axes is basically an ARVA Advanced with a third antenna to resolve spikes. As with the Advanced, the 3Axes allows you to toggle between analog and digital mode. (Don't confuse the ARVA 3Axes, which was discontinued in 2011, with the ARVA Axis, a completely new avalanche transceiver that was released in 2011.)
Searching: As with the Advanced, if you press and hold both the "-" and "+" buttons for two seconds, the transceiver switches to analog mode—not intuitive, but very functional. You can then use the "-" and "+" keys to modify the sensitivity of the analog signal (similar to a classic analog beacon). The 3Axes' third antenna resolves spikes flawlessly.
Multiple Burials: The multiple burial feature in the ARVA Advanced was updated for the 2007/2008 season. The ARVA 3Axes uses the same technique (read about multiple burials and transceiver marking on AvyRescue.com). When multiple signals are received, the icon appears on the screen and the transceiver locks onto the closest victim. After locating the first victim, you can suppress (aka "block") the current victim's signal by quickly switching from search, to transmit, and then back to search (by toggling the "nose" switch). The Advanced then directs you to the next victim. This feature worked well in my testing of the ARVA Advanced. You can learn more about searching for multiple victims in the user's manual.
Optionally, you can toggle the 3Axes to analog mode and then use the analog tones to find multiple burials (this takes significant practice).
Controls: To turn on the 3Axes, you connect the wrist strap to the transceiver. Changing to search mode is unusual, but simple—you pull the "nose" of the beacon.