You don't need a Soft synth to make the conversion.
You only need a empty midi track.
Of course if you so choose the other method but I thought I'd keep it simple.
Then you can point the midi track at any synth you like.
Keeping midi tracks separate makes it easier to try different synths.
They've made it dead simple and it works.
As said once it converts:
Open in PRV so I can see the approximate note timing.
Process transpose +12 to match the range of SI Bass
Process Quantize and whatch that the notes don't jump too far, listen.
Play through making minor edits, mostly a lot of overlapping notes and the odd false trigger, but otherwise it matches the original 99%.
I've been doing this all day converting some older backing tracks. The original real bass was played perfectly but the sound I had back then was terrible. I'm finding the SI Bass with a few tweaks sounds exactly like my Yamaha bass. The results are very good so far. It will also help even out the sound of the bass from song to song.
I'm also converting all my drums tracks to a custom kit I made by recording my own snare samples.