I've created several sf2 files, consisting of samples, instruments and presets, (is the collective name a sound font, or is that a single preset?) and for a project I'm working on, it would be easier if these were all in a single sf2 file rather than several separate ones. Is it possible in Polyphone to merge these existing files to create a single master file, or do I have to construct a new soundfont from scratch?
You don't need to make it from scratch.
You can open soundfonts side by side and copy/paste their presets.
I have explained the process step by step below, ignore it if you are familiar with it; this will help another user who doesn't know the process:
Open the Polyphone software
Click the "New Soundfont" button
Click the home button, select the other soundfont you want to open and open it
Click the arrow icon to the right of the Presets button to open the preset list.
Select the presets you want to copy. (If there is more than one preset: Hold down the Shift key and select the first and last with the mouse, or hold down the Ctrl key and select different presets with the mouse)
Copy the presets you selected with Ctrl+C.
Click the tab of the new soundfont and switch to it.
Click the Preset button and let it be selected.
Paste the presets you just copied with the Ctrl+V key combination. (Instruments and samples will be added automatically, you don't need to copy them separately).
If you have too many soundfots and want to combine them (more than a hundred, for example) you may need help from other software.