You have raws you wish to move from LR to Photoshop and back? Use Adobe's recommendation in setting up the External Editor preferences by setting Photoshop to accept a 16-bit ProPhoto RGB rendering. When you use the Edit In Photoshop command, LR will pass the rendering to Adobe Camera Raw and you'll get full resolution, high bit (16-bit) ProPhoto RGB data. From there you can edit the image, LR will catalog that new iteration. You can resample smaller and convert to another color space like sRGB for use on the web and mobile devices.