SMSL AO300 and Loxjie A40 are two other Stereo Amps with HDMI ARC input.
However, neither of them supports CEC afaik, so you'd have to use their included remote for volume control.
Edit: some more Stereo Amps with ARC input:
-Arylic B50 ($140)
-AMP25.2/AMP25 Plus ($140)
-Bluesound POWERNODE Edge ($650)
-SVS Prime Wireless Pro SoundBase ($700)
-NAD C 700 ($1500)
-Yamaha R-N1000A ($1600)
-NAD C 399 ($2200)
-NAD M10 V2 ($2500)
-HiFi Rose RS520 ($3700)