Read this document from Yamaha.
Make sure you have the latest OS installed.
The USB recording must be done in one pass....sequence everything then play the sequence out to USB. Or record real time playing to USB.
The sampler is a primitive way of recording, it's like a tape recorder. The sampler is integrated with the sequencer so you can specify where to start and stop recording the sample to do punches. Note on/off messages are added to the sequence to trigger the samples to playback at the appropriate spot.
If you screw up a recording pass, you need to do it over....punching into the middle of a sample is not possible like it is with tape, rather a new sample gets created instead. You then carefully edit the two samples to splice them together...not a lot of fun but possible. It is easy to record parts in sections using punches though, for example recording a verse in one pass, then a chorus in another, then another verse, etc. The insert effects can be used when recording samples.
Mixing capabilities are very good. 8 of the 16 tracks can use inserts, each of which is two effects which may be routed in serial or parallel. Each track has 3 band parametric EQ and two effects busses (typically one for reverb, the other for delay or chorus), plus there is a final single master effect that can be used. Mixes can be fully automated using the sequencer. If you have free tracks and enough RAM, you can do bounces by resampling.
You do have to back up all samples to external storage before powering down, but this is not hard to do. It's just slow when the total amount of samples starts to get large. Every 64MB of sample RAM gives you 6:20 of stereo sampling, mono uses half that. You cannot record a single sample longer than 6:20.
Here is a track
that was recorded with a Motif ES, using the sampler to record the guitar and bass parts as well as the sound FX at the beginning which were created using Absynth and sampled. As noted above, I did multiple takes until I got the guitar and bass parts perfect all the way through. The XS and XF can be used in the same way.