Brown 'bulbs are often dead 'bulbs, but come cymbidiums get that way, sort-of like a tan. If they are rock-hard, it may be the latter case.
Do not bother with sphag-n-bag, that new shoot will grow roots soon enough.
Also, if you want to try and get new plants from the old bulbs, you can try this:
- divide the back bulbs into individuals (being sure to leave at least 2 or 3 attached to that new growth).
- Using a tray of grade 1 perlite (the roughly 1/4" horticultural stuff sold at garden centers) about 2"-3" deep, bury the bulbs about half-way, standing upright.
- Keep the perlite moist, but avoid water standing in the tray bottom. (I use small, plastic horticulture trays, and drill a couple of small holes in the bottom)
- Kept shady and at normal temps, some of the bulbs may sprout new growths in a few weeks.