A stock question for British catering professionals
I buy tubs of Knorr stock powder from restaurant supply stores here in the uk, it's a different product from their cubes, and has a very different flavor, there's also a paste. It may be worth having a look at those. Knorr is the brand I see in the bulk quantities you'd typically see in a restaurant kitchen that you can get retail, other brands are not sold in the stores, like Brakes. 

You'll find many ingredients in stock cubes, powders and pastes to pack flavor into a small space. The commercial stuff I use has several flavor enhancers: E621 (Monosodium Glutimate aka MSG), E627 (Disodium guanylate) and E631 (Disodium Iosinate). Some have yeast extract in them. You could experiment with some MSG and Marmite to see if you can re-create that special flavor.