The question is whether you need the front suspension. If you're planning to ride rough trails and single track, then the DS is the right bike. If you're planning on roads and groomed trails, go with the FX.

But I agree with your bike-shop lady that the upper-end FX bikes (the 7.6 and 7.7) are really flat-bar road bikes. Seems to me that you would want a 7.5 or even a 7.4 for the best hybrid capability. By that I mean a wider tire (the 7.4 has 28 mm) and lower gears (while the 7.4 is a compact, it has a 50/34 up front, and 9-speed 11-34 in back, so you have that nice 1:1 ratio for steep climbs). In comparison, the 7.6 comes with 25 mm tires (great for roads, a bit thin for trails) -- it does have a nice 11-36 rear cassette though. The 7.7 is really a flat-bar carbon road bike.

I think some test rides are in order. Do you have a good LBS nearby?