Amazon Music doesn’t use “hi res” as such to describe their offerings - its lossy MP3 tracks (SD or Standard Definition up to 320Kbps) are generally served by its Amazon Music Free, Amazon Music Prime and Amazon Music Unlimited single device plans. For Amazon Music Unlimited individual and family plans, the offerings are 16bit HD (high definition) 44.1kHz or 48kHz, or 24bit UHD (ultra high definition) up to 24/192.
In terms of what any WiiM device can offer over Heos, you can play Amazon Music bit perfect up to 24/192 either via the WiiM app, by casting using AlexaCast from the Amazon Music app, or by asking Alexa. Heos can do the first via its own app, but casting or playback via Alexa via the Heos skill is HD at best, if indeed not just SD. WiiM devices can also be in an Alexa multi room music (MRM) group along with echos, which again Heos devices can’t do.