By being in z6 AND living in NE AND having a shade you are blessed with the great variety of choices of broadleaf evergreens:
rhododendrons, azaleas, kalmias, andromedas plus even larger number of deciduous shrubs that will prosper in your conditions.

Hi hostabuff - the NE forum is in the deep freeze at the moment, as Claire pointed out on another thread. But you've come to the right place, there are a lot of fabulous gardeners here - I don't claim to be one of them, but I enjoy reading about their gardens and seeing the photos.

You may have difficulty establishing shrubs hear the maples, as their extensive roots will find any amended soil you provide for the new plants. For areas near maples, try to pick plants that will be able to compete with those monsters. If you can spare the space, put your buffer plants as far forward of the maples as possible, providing a solid wall of greenery with some depth to it.

For shade in a similar situation near a large maple, I've had good luck with Euonymous 'Manhattan' - this is not the invasive "spindle tree" but an evergreen with somewhat lax stems that will grow to at least 12 feet given some support.

George has mentioned some great evergreens; you will probably get good coverage from certain deciduous shrubs too, which tend to grow much more quickly than their evergreen counterparts. Although they are naked in winter, the ones with dense branching structure like viburnum, wigela, deciduous holly, and tall hydrangea (ie Tardiva) give nearly complete privacy and a sense of enclosure.

My current favorite conifer is Japanese umbrella pine - it's a slow grower, but has a really lovely texture. I also like the native evergreen hollies, which are excellent bird habitat and provide a great green screen. Most of mine are volunteers, and they do grow quite fast when self-sown. They can get really wide, which might be a problem eventually. I've also used the ubiquitous upright yew successfully in deep shade along a couple of borders where I have limited space. It's not as interesting as most needled evergreens but it certainly is reliable and it does handle shade and neglect well.

If by "not a hedge" you mean that you want to plant a wide variety of plants, that's a good idea. One side of my back yard has a long row of spruce, and I've seen the down side of relying on a single species for cover; when spruce spider mites attacked, I nearly lost that entire section of my buffer planting. The opposite extreme, one of each of many kinds of plants, also has some drawbacks because it can look haphazard and overly busy. I now usually aim for a mixture of a limited number of species with repeated groupings of plants of one type.

I hope we'll hear some advice from other members here, there are quite a few regulars who often have great design ideas.

Hosta,
I have had very good good luck under maples with Pieris and a Variegated Euonymous not nearly as nice as the one described by dtd. I was not as lucky with azealas or rhody's. The dry deep shade of Maples is why most landscapers use them for street trees only they can be a challenge. Keep in mind that many if not most evergreens will grow in different degrees of shade but will tend to be a looser/leggier form from reaching for the sun. I love the informal look of some of my Holly's that are happy in the shade. For a little kick of color don't forget Hydrangeas, or clethra for a sweet scent, then of course more viburnum's than I can count . Well hopefully as the forum become more active you'll hear from some of the real gardeners. kt