The current range of Arcam AVRs-- including the AVR390, AVR550 and AVR850, as well as the AV860 AV Processor-- receive IMAX Enhanced certification, meaning they meet the "stringent" standards set by the recently announced certification program.
IMAX Enhanced was launched back in September 2018. It involves a certification committee of IMAX and DTS engineers, plus technical specialists from Hollywood. Receivers bearing such certification should be able to deliver IMAX digitally re-mastered 4K HDR content and IMAX signature sound mixes delivered by DTS.
An IMAX Mode should optimise the decoding of DTS:X audio to make use of the dynamic range offered by IMAX theatrical sound mixes, before delivery via proprietary DTS:X codec designed for home use. On launch, the program got backing from Sony Electronics, Sound United (the Denon & Marantz parent company), Sony Pictures and Paramount Pictures.
The above mentioned Arcam AVRs should receive IMAX Enhanced capability via free firmware update. January 2019 should see products from Marantz and Denon receive a similar firmware update, specifically Marantz AV8805, SR6013, SR7013, SR8012 and AV7705, and the Denon AVR-X4500H and AVR-X6500H AV amplifiers.