The 3806 will passthrough 1080P via HDMI. It has analog to HDMI conversion but with no scaling or deinterlacing so you'll get 480i analog in, 480i HDMI out, 480p analog in, 480p HDMI out, 720p analog in, 720p HDMI out etc etc. The output resolution will always be the same as the input resolution. The next model up (AVR4306) does have scaling and deinterlacing, albeit up to a maximum of 1080i (output via HDMI).
If you're after 1080P scaling from analog sources to HDMI then you need to move up to the 4806CI or 5805CI.