Thanks. I guess if the enzyme does not work it is time for Barabasol or Burma Shave.
What you have is a commercial grade rubber-backed carpet and the 'brown tinged' areas are from too much cleaning/rinse solution which causes 'wicking' up of fine particles of dirt to the top of the fibers that remains as the water evaporates.
The rubber backing prevents the moisture from going anywhere but 'up' and these talc-sized particles are carried up and deposited on top. Easy to remove, and a 'buffer' system is best when this occurs (happens alot when too much solution is used on this type of carpet).
I own two Chem-Dry franchises in N. California and can highly recommend the 'dryer' cleaning method (hot carbonated extraction) over typical 'steam' cleaners- plus, our pre-sprays aren't as soapy (9.5 pH vs some much higher used by steam cleaners).
A pH higher than 9.5 will destroy any stain resistence and isn't recommended on today's 'fifth-generation' nylon carpets.
Home Depot bought the Chem-Dry company in 2006, but each franchise is still family-owned-and-operated. You can go to Chem-Dry.com and use the link to find the nearest franchise (zip code locater). Look at those who pop-up and steer towards those with a 5 Star Tech rating. Call and ask if they do Home Depot warranty work ('cause if they do, they'll be the best in the area and you'll know they've been cleared by Home Depot's background checking and can be trusted in people's homes). You could have Home Depot schedule the appointment for you, but I think you'll get a better quote if you talk directly with the franchise.
The areas in front of the desks may be damaged by the wheels on the chairs and may not be restorable- those 'protectors' really help against crushing the fibers. Heat in the cleaning process will help as nylon is fairly resiliant and the heat helps it bounce back.
This is a busy time for most carpet cleaning companies. If you can book a week or more out they'll really appreciate it. Hope this helps.