Here's my take on things from a professional DJ's point of view:
1 - The distorted mic issue meant under no circumstances could I use the mic live. Same problem with top of the range Sennheiser and Beyerdynamic mics. The fix with adapters works to a point but is cumbersome and defeats the compact nature of the unit. Unusable.
2 - The low volume output is a design flaw and for this units should be replaced. what's the point of buying a "standalone" unit then having to route the output through another mixer to boost the volume?. In my club for example I had to overdrive the output to get anywhere close to other mixers and red line everything with the resulting distortion. Unusable.
3 - Low headphone output is sort of acceptable depending on the type of headphones you have but still not acceptable. I found with my HD25 headphones it was OK but with the Pioneers which I prefer to work with the output was too low.
4 - Build quality issues. Switches not working, LED's at different brightnesses and grinding jogwheels. AA justify this to keep the price down. I don't get it.
Although I returned mine within the first week and got a full refund, I really feel for anyone else with a MK1 unit. AA should replace the unit as I personally feel it is unusable, others may have a different opinion.
P.S. The MC6000 is a hundred times better. OK, it is a lot more expensive but you get what you pay for. It did have an initial issue with VDJ but it was fixed in 3 weeks. Denon realise people buy these units to work with and fixing issues are a priority for them.
The VMS4 is probably OK for low grade mobile DJ's working through cheap amps and speakers but that's about it.