Hmmm, how to explain it in a quick way, I guess it takes longer (sorry if I bore the hell out of you):
1.) YASE was developed to let the Fantom act as a Sampler:
For many users the internal sounds are not enough - they require a possibility to add sounds - thats one reason why you plug up to 1 GB RAM into the device. For the playing of internal sounds you don't need to do this.
Additional samples? Nice feature - but Roland forgot to make the handling of such samples (to bring them into patches, with key ranges, root note, velo-ranges, ...) as easy as a musican expect this. To import such data you can waste hours of programming until you listen only one tone =)
And YASE simplifies the handling of additional samples, with the assignment to multis, patches a.s.o. - From hours downto few clicks...
--> For internal sounds you need Rolands PC-Editor, for additional sounds take YASE - means: YASE does not act as a replacement of your PC-Editor, it is an extension.
Thats why one of the most powerful features is the import of (additional) samples of AKAI or Roland CD-ROMs with patch-, multi- and other information of the source data.
The PC-Editor of Roland communicates directly via MIDI-Sysex-Data with the Fantom, YASE doesn't "communicate", it changes files, which will be loaded during the booting procedure.
Please note: You have to reboot the Fantom if you make changes via YASE.
2.) YASE only handles external samples/patches/multis. Means - YASE can only access the USER and the CARD memory of your Fantom, via a file access. This access cannot "see" internal samples/multis/patches (INT1/INT2), they are stored inside the hidden ROM - no access possible for YASE.
3.) The .mul file contains the above mentioned additional samples next to the key assignment rules. YASE grabbs the samples and stores them in a YASE-own format. This is the reason why the samples are available even if you import them into an other device.
4.) The SVD file neither contains samples nor other assignment infos. Internal samples (BANK PRST) are "burned" into the ROM, as mentioned above.
If you want to know more please download the Trial version of YASE and open the Help File (F1), there you'll find a lot of additional information regarding the topic Memory Locations and Access. It might be helpful to understand much better the physics of your Fantom device.
Best Regards -
Jens.