Frank,
First a couple of comments regarding memory. There are two
different types of internal memory, and then there are the USB sticks. The internal memories are:
- User memory (or user drive): this behaves exactly the same as the USB stick, and in computer terms, it would be a different hard drive. Here, you can store whatever you want (styles, registrations, MultiPads, text files...). Whether you hold your content here or in a USB drive is mostly a matter of preference and convenience. Unlike in previous models, the amount of available space is reasonable (1GB for the SX700, 4GB for the SX900), and the style/registration/multipad files are relatively small.
- Expansion memory: this is an internal, fast memory, connected directly to the sound generation engine. This memory is optimized for holding samples that are to be reproduced by the instrument, and is not accessible from the user interface. This memory does not behave like a disk drive at all. This is where the samples from external packs (YEM) will be loaded into. There is no way to hold them anywhere else, as the required bandwidth to read the data and generate sounds, with a 128 voice polyphony, is simply not there (for comparison, the USB stick's bandwith is taxed just playing a standard stereo audio file!) For the SX700, you have 400MB of available expansion memory (1GB for the SX900), which is really quite a lot. Many older-generation keyboards had just this (or less!) to hold the samples for all the internal sounds!
For older-generation models, the recommendation was to keep the user drive mostly empty, and to keep everything in usb sticks. The main reason for this was the extremely limited amount of space in the user drive (for example, on a PSR-S950, we had just 6.7 MB - yes, MegaBytes! - of space). Therefore, the common wisdom gleaned from that era is to use exclusively usb sticks. This would still apply to the SX600, where the user drive is limited to 20MB.
Today, for the SX700/SX900, I would re-think it. I would definitely keep copies of everything on one (or more!) usb-sticks, just in case the keyboard stops working, but other than that, I would tend to keep the things I most commonly use on the user drive. Another possibility is to use the user drive while editing, and to copy the final version (of styles, registrations, midi files, and so on) to the pen drive. Just find a way that works for you, but be consistent. Consistency is more important than having an "ideal" way of doing things.
Regards!
AFP