Can you play a midifile thorough a workstation (via connected laptop) but play a sound on the keyboard not in the midifile? And if so, how? Thank You.
Yes, this is definitely possible. What you want to do is hook up that keyboard/synth via MIDI to your computer, and set the MIDI out to the MIDI that goes to the keyboard.
In XP, you can find this under Control Panel, Sounds and Audio Devices, the Audio tab, and down towards the bottom, MIDI music playback. Change the default device. Once you've done this, play a MIDI file with just about anything, and your keyboard will handle it.
Sequencer software will often use its own independent MIDI configuration, so if you are using something more than a typical media player, check its settings for the primary MIDI out to use.