I'm interested in hearing from those that do this and what techniques they use for adapting the parts to bass. I find that it depends so much on the music. Some thoughts: Sometimes you can play the cello part as written (sounding 8vb). However sometimes it's better to play it 8va (where it would actually sound on cello). In some cases, it's nice if you have a repeat to play it differently the first and second times. Regardless, it is certainly nice to be able to play 8vb (especially with an extension) for certain cadence notes or even just the final note. Too much low stuff (which includes playing too much of it as written which is of course 8vb) reduces the effectiveness of the low notes and can definitely sound inappropriate especially if it is all around notes on the extension. You shouldn't necessarily play up the octave even if you can. For me, especially on unwound gut G and D, the G runs out of steam at about high C or D and even before that, the sound is just not right for "bass line" playing. Generally I will try not to play higher than the G harmonic when playing this kind of stuff.