I grew Dicksonia antartica and D. fibrosa for many years under my moso grove, but eventually had to relocate them to another shady location because the bamboo was too strong a competitor for the tree ferns. Tree ferns need continuous moisture and lots of nutrients to thrive and the bamboo rhizomes were sucking too much of both for the tree fern's root zones for them to thrive.

Keeping the culms thinned 2-3 feet apart to reduce the bamboo grove's competition for the water and nutrients in the grove will help your understory plants to thrive. Basically any plant listed as growing well in dry shade would be a candidate as a bamboo grove understory plant.

A partial list of plants growing in my moso groves:
Aucuba japonica
Fatsia japonica
Rhodea japonica
Camellia japonica
Cephalotaxus harringtonia
Aspidistra eliator
Trachycarpus fortunei
Sabal minor
Hedychium coccineum
Clerodendron bungei
Magnolia virginiana
Podocarpus macrophyllum
Dryopteris erythrospora
Mahonia x media
Mahonia bealii

I think Calanthe Orchids would make a choice and showy albeit expensive option. But I wouldn't wait too long as they need several years to get going as well.

Danae racemosa might look a little exotic too.

Asplenium platyneuron is a drought tolerant fern.

I love my Rhodea collection, but hadn't thought to put any with my boo. Thanks for the idea, Mike.

Yeah, I'm growing rather keen on my Danae racemosa idea. The orange berries would look very tropical against the yellow in your 'Castillion'. Might make an interesting combo with P. Nigra around Halloween as well.

Last night I drifted off to sleep with persistent thoughts of Remusatia vivipara, or "Hitchhiker Elephant Ear", in connection with this post and thought I better post early before I lose more sleep.
I don't know an awful lot about this plant, but if I were in your zone I would certainly do some further research. What I can tell you is that you should expect big elephant ear type foliage- can't get much more tropical than that- and a shade tolerant plant. I would think the plant could handle drier soils, especially in humid Louisiana, considering that it is found as an epiphyte in the wild. The last thing I know about this plant is that it puts up above ground bulbils from which it can be propagated, which sounds ideal in a bamboo grove where division by digging might eventually be problematic.