High density surface EMG as described in the recent publications on the Biosemi site is possible with the addition of the sEMG accessories. The original model of the high density sEMG probe was made for ActiveOne, so the connector differed. The current version separates the electrode grid from the preamp as in:
reusable grid
sEMG preamplifier
Less dense sEMG can be accomplished with an elastic fabric with electrode holders like the EEG cap stretched over a muscle.  This would need to be custom-made, but would not be expensive.
Fine wire EMG would require either spring contact adapters or safety socket leads with inline active headstage. If your fine wire electrodes will be stripped but unterminated, you need spring contacts, and if your electrodes terminate in safety sockets, you need inline adapters.