Cycle through available audio devices with key binds(a,ctrl+a). Change "wasapi" on line 1 to your relevant audio api.

cycle-adevice.lua

local api = "wasapi"
local deviceList = {}
local function cycle_adevice(s, e, d)
	while s ~= e + d do -- until the loop would cycle back to the number we started on
		if string.find(mp.get_property("audio-device"), deviceList[s].name, 1, true) then
			while true do
				if s + d == 0 then --the device list starts at 1; 0 means we iterated to far
					s = #deviceList + 1 --so lets restart at the last device
				elseif s + d == #deviceList + 1 then --we iterated past the last device
					s = 0 --then start from the beginning
				end
				s = s + d --next device
				if string.find(deviceList[s].name, api, 1, true) then
					mp.set_property("audio-device",deviceList[s].name)
					deviceList[s].description = "•"..deviceList[s].description
					local list = "AUDIO DEVICE:\n"
					for i=1,#deviceList do
						if string.find(deviceList[i].name, api, 1, true) then
							if deviceList[i].name~=deviceList[s].name then list = list.."◦" end
							list=list..deviceList[i].description.."\n"
						end
					end
					if mp.get_property("vid")=="no" then
						print("audio="..deviceList[s].description)
					else
						mp.osd_message(list, 3)
					end
					return
				end
			end
		end
		s = s + d
	end
end

local function cycle_back()
	deviceList = mp.get_property_native("audio-device-list")
	cycle_adevice(#deviceList, 1, -1) --'s'tart at last device, 'e'nd at device 1, iterate backward 'd'elta=-1
end
local function cycle_forward()
	deviceList = mp.get_property_native("audio-device-list")
	cycle_adevice(1, #deviceList, 1) --'s'tart at device 1, 'e'nd at last device, iterate forward 'd'elta=1
end

mp.add_key_binding("a", "cycle_adevice", cycle_forward)
mp.add_key_binding("Ctrl+a", "cycleBack_adevice", cycle_back)