The 6600 is a great machine ... I loved mine.
The only reason I do not have it is that I wanted a bigger throat space. I never thought I would get to like FMQ or even straight line machine quilting at all, but the 6600 spoiled me and got me hooked! So you might want to take that into consideration before you make the final purchase decision, and consider whether a further upgrade would be of interest.
Best to find out first as to how the warranty would play out for you if you purchase it on the internet.
Also, who will service it? My Janome dealer will service machine they have not sold, but at a different rate and priority level. This may not be the same for all dealers, so know up front. And too, machines purchased direct from them, they offer free servicing for # years. That could soon make up your price difference.
The machine is not hard to learn ... although I am a firm believer in taking advantage of the classes offered and to have the availability of a local dealer to take care of you if you do have problems.
Easy enough said by me ... as I have a great dealer, who is always there for support and service, long after the classes are had and the warranty is over. That is one reason why I have been a four-time-repeat buyer there.