Keep in mind that the younger, more viable rhizomes will likely be located on the outside edge of the grove and the older ones toward the interior. So you might want to think about preserving the outer area/edge that you'll see the most and culling the interior - if that makes sense.

Personally, I use hand bypass pruners for this it ends up being more efficient than a machette, that or a blade on a 'string' trimmer if you have one.

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Brad Salmon, zone 5b/6 Southern Indiana
Winters -20 to -25C. Summers 30 to 35C , humid. 115 cm annual precipitation, frost free from May through early October. 259.3 meters elevation. Growing 150+ species. http://www.needmorebamboo.com/

I did use bypass pruners, they worked awesome.

The only thing is, how do I preserve the outer edge when I need to cut the outer edge back?
Right now the grove is nearly perfectly round and ~25-30' across... I need to get it down to 15-20' across.

Thanks again for all the help!