I just measured 18.5 inches including the large volume knob in front and the binding posts in back, so 19+ to be safe, which coincides with 50cm as Chris mentions. You will want to have some extra space for your cables of course. I'm currently 20.5" or 52.7 cm from wall to end of front volume knob. For 2. I have a Klipsch SW-311 hooked up to the AS-1100 via the Pre Out jacks in back. According to the manual: The PRE OUT jacks output the same channel signal as the SPEAKERS L/R CH terminals. • When you connect a stereo cable to the PRE OUT jacks to drive the speakers using an external amplifier, it is not necessary to use the SPEAKERS L/R CH terminals. • The signal output at the PRE OUT jacks are affected by the BASS and TREBLE control settings. You can find the A-S1100 manual here: A-S1100 - Downloads - Yamaha - United States Page 17 shows an image of a sub connected to the PRE OUT. They are standard RCA jacks.