I've just tested loading a Virtuoso voice with sample into the MoXF: As I feared, the slow strings I tried abruptly stop sounding after about 2 seconds. The waveforms are wrongly implemented as one shot samples...

Luckily, a few waveforms of the strings part of the package are looped (e.g. Marcato strings) and also implemented as stereo samples, so probably they will indeed be a valuable supplement to my MoXF strings. But most waveforms seem to be unusable due to this one shot problem, unless I change thousands of keybanks into loops myself (with the problem of avoiding these lound popping noises).