No; let me try to explain it again.
You know that the General MIDI standard defines 128 instruments: Acoustic Grand Piano, Bright Acoustic Piano, and so on. These instruments are used in MIDI files, and are selected by "Program Change" events (MIDI event $Cx). Of course newer standards such as the Roland GS and the Yamaha XG expand the instrument selection by using two MIDI controllers, but this doesn't matter for what we're going to do here (e.g. we can consider Roland GS's Synth Bass 3 to be instrument 38 just like Synth Bass 1); if you want to know more about this I'll be glad to talk about it, but I don't want to make things harder than what they are.
Back on topic, this fixed set of instruments is different than what we have in XM files, where everyone can use random instruments numbered in any way, which means that all the instrument mappings can be done once and for all instead of being redone every time you convert a file like you did with XM files, which is why the instrument assignments are now stored in the GYB file itself unlike X3V files which only contained instruments without any assignment.
So, once you create a GYB file, you might as well keep it forever and forget about it. What you have to do, once, is to populate it with your FM instruments, importing them from various formats such as TFI, and then you manually assign those FM instruments to one (or more) GM instruments.
Say that one of the instruments you imported is "My super happy Synth Bass!.TFI"; of course you want it to be used for Synth Bass, so you select "Synth Bass 1" from the GM instruments list, and then you select "My super happy Synth Bass!.TFI" from the FM instruments list. In this way, every time you'll convert a MIDI file which uses Synth Bass 1 (or Synth Bass 3, or any other GS/XG variations over that), you'll get an SMPS file which uses My super happy Synth Bass!.TFI
Of course you don't need to assign all the 128 GM instruments to something, as some of them are rarely used if at all, and I doubt you're going to convert a MIDI file which uses the Helicopter instrument or something; focus on the ones you're more likely to need, and keep in mind that you can use the same FM instruments for several GM instruments if you're lazy (you can assign My super happy Synth Bass!.TFI to Synth Bass 2).
Vice versa, the fact that you can store 255 instruments in a GYB file also allows you to keep spare ones in case you need more variety, so if you feel like using "Another great Synth Bass!!!.MVS" for a particular conversion, all you have to do is to change the assignment from the aforementioned comboboxes.
I hope this is a bit more clear.
edit: here you are a couple of screenshots of the instrument editor:
The normal view. You can create new instruments, or import them from files. When you click on an instrument from the list (in this case, "Pan Flute"), it shows you all the parameters (detune, multiple, ...) for that instrument, which can be edited and previewed on the fly. This screenshot also shows that the GM instrument "Electric Bass (pick)" has been assigned to the FM instrument "Picked Bass" (which you can't see on the list because it's somewhere offscreen, but it's there, otherwise it wouldn't show up in the assignment combobox).
When you import an instrument, you can view its parameters and preview it, but you can't edit it until it's imported. You have the option to mass-import all the instruments from an YMX or a X3V file.
This is basically it. I am going to upload those pictures on the wiki and write a small article about the editor as soon as the site will be responsive enough to let me preview the page in a decent amount of time.
This post has been edited by nineko: 08 June 2011 - 08:51 AM
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