Monitor XT90 Dolby Atmos Certified Height Speaker. Polk Monitor XT90 Atmos Speakers Specifications. XT90 Specifications. Works with Any Dolby Atmos or DTS:X AV Receiver. To use the MXT90 as a height channel, match it with any A/V receiver (4 or 8 ohms) that provides a minimum of seven channels and that supports the Dolby Atmos, DTS:X or DTS Virtual:X formats.