The 705 does have an adjustable mute level that can be set as high as -10db I believe.
While it doesn't seem likely that this would affect the minimum volume as controlled by the remote or volume knob, it may be worth the time to check where it is set. Possibly changing it to the infinite, fully muted, setting.
As stated above, you'll need to go into the volume set-up. Page 92 of the manual.