By default, LinnStrument is set up to send on MIDI channel 1 with a pitch bend range of two semitones. This allows it to immediately work with the standard presets of most synthesizers, which are optimized for the on/off switches of standard MIDI keyboards. LinnStrument will also send polyphonic pressure messages and Y-axis movements over Control Change 74 messages, but these standard synthesizer presets usually won't respond to these advanced messages. However, those presets are optimized for the limited expression of MIDI keyboards, so you'll notice some limitations, which are listed below along with instructions to modify the preset sounds to correct those limitations:
For longer pitch slides, increase the Pitch Bend Range of both your sound generator and LinnStrument. In LinnStrument, change "Per-Split Settings > Bend Range". A range of +/-24 semitones is ideal for LinnStrument (in order to slide across the entire surface), but many sound generators permit Bend Range up to only 12 semitones.
You'll need to assign your synth to respond to LinnStrument's pressure messages, usually to control note loudness. By default, LinnStrument sends pressure data using MIDI Polyphonic Pressure messages, but it can also send either Channel Pressure messages or any Control Change message.
Note that in a MIDI keyboard, pressure (aftertouch) is sent only after the key is fully pressed and the note is sounding, and therefore is not useful for controlling the overall volume of each note from silence to full but rather for adding an extra effect to a note that is already sounding. In LinnStrument, pressure (aftertouch) messages are sent continuously from the lightest to heaviest touch, and can therefore be used to continuously control the overall volume of each note from silence to full level, analogous to wind pressure on a wind instrument or bow pressure on a bowed string instrument. For each reason, it is useful to create sounds that use pressure to continuously control note volume from silence to full.
To add Y-axis response, you'll need to assign your synth to respond to LinnStrument's Y-axis Control Change 74 messages. By default, LinnStrument sends Y-axis data using Control Change 74 messages, but this can be changed to use any CC number.
Often people initially make the mistake of thinking that Y-axis should be used in the same way as Mod Wheel, adding LFO modulation. This is not a good idea because one of the main purposes of expressive controllers is to replace the venerable and unnatural LFO with performed gestures like vibrato (left/right finger movement) or tremolo (varying pressure). Instead, a better use of Y-axis is to provide a continuous change in timbre, analogous to picking a guitar or bowing a violin at different string positions between the bridge and neck, or varying embouchure on a wind instrument. A good example of this in subtractive synthesis is to assign Y-axis to vary the pulse width of a pulse oscillator, thereby providing a continuous change in the fundamental harmonic content of the waveform in such a way that all tones produced are useful. In this way, timbral variation becomes a performance gesture.
To add this, you'll need to use a sound generator that's compatible with the new MPE standard, with each of its voices receiving on a separate MIDI channel. And you'll need to to set LinnStrument's Per-Split Settings > MIDI Mode to "Channel Per Note" (which sends each note on a separate MIDI channel). If starting from scratch, it's best to use MPE-compatible messages for the Per-Note Channels: Pitch/X = Pitch Bend, Y-axis = CC74, Pressure = Channel Aftertouch.
To see a list of MPE sound generators, go to the LinnStrument Support page and click "MPE/Expressive Sound Generators". If you're on mac, our best MPE sounds are in our downloadable sounds file for Logic or MainStage. Or you can use Bitwig 8-Track, which is included with your LinnStrument and which includes a vareity of MPE sounds.