You can get a midi splitter. Basically, it just divies up your midi lines. So if you only have 2 in/out, it will change it to 10in, 2 out or 2 in, 10 out but these lower the amount of channels the midi can carry. So if you use a 1 to 8 midi splitter, you only get 2 channels of midi in each line.

Your best bet would be to get a larger midi interface, or maybe find a PCI card midi interface.

As far as i know, you can't just plug in another one into your current one. I might be wrong though.

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