[jamesperrett]

Looks like Presonus have skimped on those instrument inputs. Most manufacturers offer switchable line/instrument settings on the jack inputs. If you keep the cables to the interface as short as possible you should be OK using the instrument inputs provided that the output level from your cassette deck isn't too high.

As colourking says, for best results you need to match the playback head azimuth to each cassette - I find that this makes a big difference to the end result. And as Paul says, keep the level reasonably low when recording because you never know when an unexpected peak might come along. For reel to reel tapes I set 0dB on the deck's meters to -18dBFS on the digital side but you may get away with a little less headroom with cassettes. If this is too quiet, you can always process the files afterwards to bring the level up.