Does BioSemi produce an amplifier that we can use with our existing AD card ?

No, the ActiveTwo system is a fully digital system. All electrode signals are amplified and digitized in the isolated amplifier box located close to the subject. From then on, all signal processing is digital. This setup ensures the best possible subject isolation: we only need a single optical fiber, whereas most of the competition needs an analog isolation amplifier per channel. Especially in systems with a high number of channels, all these parallel isolation barriers add up to a high capacitance. This leads to unacceptable leakage currents, which inevitable will lead to interference and safety problems.