Are they big trees with a low canopy or a high canopy (limbed up) because the extra light will increase your options.
With 120 year old silver maples and high canopies, I have had success with:
Eleutherococcus sieboldianus "Variegatus"
Ribes sanguineum (Flowering Currant)
Hamamelis virginiana and H. x intermedia (Witch Hazel)
Forsythia viridissima "Kumson"
Kerria japonica
Buxus (Boxwood)
Mahonia aquifolium (Oregon grape holly)
Symphoricarpos albus (Snowberry)
Aesculus parviflora (Bottlebrush Buckeye)
Euonymous alatus (Burning Bush - it doesn't do much burning in the shade though)
Abelia mosanensis
Paeonia suffruticosa

High or open shade has been critical for all of these. Low or dense shade will not end well.

Undoubtedly there are others but these are mine. All are planted under the maples and compete with a thick mat of maple roots (ie. bone dry). I helped them for the first few years with irrigation and despite that, growth was slow. After 3 years or so, they were able to compete (growth accelerated) without irrigation. I would not use any fabric (maple roots grow through it anyway)....to much work, not enough benefit.

These ones failed - mainly lack of moisture, some b/c of light:
Oak Leaf Hydrangea
Paniculata Hydrangea
Hydrangea arborescens
Carolina Allspice
Ribes odoratum
Viburnum opulus
Ilex x meserveae