I never used old brown. Instead I just added more restrainer; both potassium bromide and sodium chloride work well. Sodium chloride gave me more brownish/pinkish hues on Fomatone; bromide leaned more towards tan and yellow. I used a highly dilute and simple developer (just hydroquinone and a tiny amount of sulfite), used it one shot, and added restrainer to taste.
You can also add a little sulfite to your developer to slow it down; this will make things more colorful up to a certain point. If you add too much sulfite, you no longer get infectious development, so it's a little tricky. I preferred adding bromide and/or chloride.
What also boosts color is if you develop partly in a neutral pH metol-only developer (which is really slow and will grown very tiny silver crystals) and then boost the shadows in a normal lith developer.
Moersch sells whatever you need in convenient bottles with clear instructions. DIY mixing also works quite well, but is of course more complicated.