I have owned an Ac-6 for almost 3 years now. It is actually my main gigging bass. The bass is amazing! I would take it hands down over anything else. It is such a sensitive and expressive instrument. I don't touch my controls after I make my initial settings. There are so many different tones available depending on how and where you pluck the strings. With that said, here are a few things to keep in mind.
When I first got it I almost felt that I got in a little over my head. The strings tend to respond more like an upright would and the electronics translate everything you do to the amp. I prefer this, but this is not a forgiving bass. This bass will point out every flaw in your technique. I personally think that is a good thing because it makes me practice.
The other little pet peeve I had is that I don't like having every fret above the 12th marked with a dot. I would get totally lost up there. What I did was color them over with a sharpie and then seal that with a little drop of clear nail polish. Without the sharpie, the dot would show again after a gig or two.
As far as string go I have only tried two different sizes of LaBella's. You need to use the taper core strings that the bass is designed for or your action will be all wrong. I have had the same set of strings on this bass for more than two years and I can still play harmonics at between the second and third frets. I have never seen another bass that can do that with strings that are that old. I am also a dedicated new/bright string buy (Dean Markley Blue Steel) but this thing sounds so good I can't find a reason to change anything.
If a bass doesn't feel like the perfect fit, then you have two choices. Either you can pass it over or play it. If you play it enough, it will become the perfect fit. That is what happened to me with this bass. When I have tried to explain this bass to other people I put in terms of cars. This is not a Ferrari, this is a Rolls Royce. And when it comes time to steer it into the corner you better be prepared or it will kick your ass.