That's the raw Bayer <=> raster bitmap conversion I'd avoid doing more than once because you need to interpret the image each time you do that (details below). Moreover, if those conversions are done by two different tools, I doubt it's consistent. I think that once you're in raster bitmap, you should stay there and avoid other tools that prefer working on Bayer. If you must do it, you should at least take a 16-bit colour format and avoid lossy compression, but expect those files to be quite big. So indeed, don't save as JPEG, but 16-bit TIFF should be fine.
That being said, I'm not 100% sure but I think that most of the colour adjustments, cropping, geometry transforms, etc, are performed on raster bitmap, so it should be safe if you stick to those operations once you're in raster. Tools like Rawtherapee and Darktable make it visible, but other tools like Adobe's hide that from the user, so it's less obvious. There are normally just a few operations that are performed on the raw format before demosaicing; for example, if I understand well their confusing website, DXO's denoising is done on raw.
Doesn't DXO PhotoLab have all the necessary tools anyway? When I briefly tried it, it lacked a proper vectorscope for colour grading (which not everybody uses), but otherwise seemed to have all the necessary features.
PS: Since I'm not sure everyone is familiar with the details:
raw Bayer is the 2x2 RGGB (or variant) pixel arrangement in DNG, NEF, ...
Raster bitmap is the classic image with RGB pixels like in JPEG (8-bit colours), PPM, PNG, TIFF (8 or 16-bit colours), ... Transforming one of the R, G, G, B single-colour pixel to one full RGB pixel - demosaicing - requires some interpretation based on the surrounding pixels, and there are many different algorithms for that, as there are many different sensor colour filters for those R/GG/B colours, meaning they're not exactly the same RGGB colours on different cameras. That's why going back & forth can't be too good, in my opinion.