I can run 10x 2pac's on an old hardkernel ODROID-X. This also ran +-50-70 gridseed orbs, 2x pepper miners and 5x one string miners at the same time back in the day with chained USB hubs, but limited to 2 chains. It is the best dev/mini board I have used to date. I have tried a newer hardkernel C1+ device and it can't run anything for longer then 5 min and just hangs.
BBB, are ok and also have USB issues, except with the gridseed blade and pepper miners. I used to run 10x blades on one BBB and never even had one lock up or issue on debian, it also doesn't like USB hub chaining.
All of the above are always headless.
Pardon my newbness for two secs... but by headless do you mean that you don't fully enclose them?