Ask Mr. Smarty Plants

I know that you are thinking that a fast growing tap-rooted tree is just the thing to fill an empty space (or hide something you don't want to see) in your garden without impacting and competing with the existing tree and perennial garden.  However, fast growing deciduous trees are usually pioneer species which means that they are generally weak wooded and short lived in order to make way for more durable species.  Also, all trees that are known to be tap rooted when young (which makes them more difficult to transplant than more fibrous rooted species) still have feeder roots that extend well beyond their drip lines when mature.

For those reasons, I would recommend you consider a smaller (12-36 ft) ornamental tree with good fall color.  You are right that Liquidambar styraciflua (Sweetgum) can have amazing fall color, but it will get much too large and there are only so many "prickle balls" a crafty person can glue into a pine cone wreath.

Here are some trees in that size range (native to your area) for you to consider.

Amelanchier laevis (Allegheny service-berry) (here are some fall color images)

Asimina triloba (Pawpaw)

Cornus florida (Flowering dogwood)

Crataegus marshallii (Parsley hawthorn)

Cyrilla racemiflora (Swamp titi)

Nyssa sylvatica (Blackgum)

Oxydendrum arboreum (Sourwood)

Sassafras albidum (Sassafras)

Sorbus americana (American mountain ash) (more images)

These have been selected based on potential fall color and size only.  You will have to determine if your conditions will meet their cultural needs.  Because there is much color variation within a species, you will want to wait until the trees in the nurseries have started their autumn display to select the "best" one. Even then, your tree may color differently once it is planted in your garden.