Hi @klavierpunk, depending on the usage (you have always the same instruments load, for your practising?) you can set the MIDI transposition in Halion Sonic first for every slot (for example: +1 semitone), then save a new Endpoint Configuration with this settings (called seething +1), then duplicate your used Playback Template, edit it, add “+1” at the end of the name to recognise it, import the new Endpoint Configuration and move it on the top of the list (the instrument contained in it will so have the precedence). And when you want to hear all +1 semitone higher, you can just switch and Apply the new Playback Template. You need a new Endpoint Configuration and a new PT for every interval that you need to switch to, and it will work if the used instruments are the same as your initial setup), but is pretty fast to switch PT ;-).
@klavierpunk
I don’t quite understand why the Transposing function is cumbersome? Possibly because the notes and key change, and you need all to remain in the original displayed key? You could duplicate your project and transpose the duplicate and playback it, while reading the original project.