Doh!!!...and I have been grinding my teeth over this one for the last 24 hours! Ever the 'Tweak-Freak' (go on...hold your hands up the lot of you - I KNOW that I am NOT alone!), I had been 'fiddling around' (as you do) and, to my total dismay and disbelief yesterday evening, I suddenly discovered that my PMDG First Officer was either asleep, had 'done a runner' (who could blame him ) or had been stricken down with a severe bout of Laryngitis! Ergo; No amount of verbal coaxing would get him to reply to anything beyond the usual courtesies of 'setting up'. In that state of laconic desperation that descends upon all of us FSX'ers I tried to recall every fps-enhancing 'adjustment' that I had made on the previous evening... a task made immeasurably harder by the self-induced alcoholic amnesia... and I went through all of the well-known remedies - short of a full Windows ReInstallation! In desperation (and on hold to the Samaritans), I restarted FSX for the umpteenth time, poured myself a consolatory glass of chilled, selected the Maul as the default aircraft and resigned myself to listening to the wonderful burble of the engine as it ticked over - a truly wondrous sound coming through the 250Watt Hartke 1x15 Bass Cabinet that sits adjacent to my Flight Deck.... Somewhere between the third and fourth 'slurp' [acknowledgements to the late Keith Floyd], it suddenly dawned on me that a stereo output into a single channel input is going to lose something along the way? I looked at my lappy audio-out socket. Yup. A Stereo Out. I then looked at the Hartke Amplifier Input Socket. Yup. Mono. Result? I unplugged MY idea of 'Audio Nirvana', reverted to my crappy BenQ speakers and - lo and behold- my erstwhile AWOL First Officer has returned to active duty. (Boy! - is HE going to get some rough rides for the forseeable)!!! The Lesson for Today? If you are having trouble with your F/O ... just be aware that the audio output on FS2C is a STEREO feed and does NOT like being chanelled through a Mono setup! OK! 'nuff said. Take me out the back and shoot me now. Dave Corbett.