if you check the credits on "Rumours" you'll see that they mention Fatbox DI's. i first heard about that from an engineer who owns several Fatbox DI's when he was telling me how good they are. apparently, when you bought them you had to give each one a name & that name was engraved on them. he said they were quite expensive. i'm now minding a couple of them while he is overseas & i love 'em. i don't know if you can still get them, i've been unable to find out any information on them, & the electronics are sealed in goo, so i don't know how they're made.
i can assure you that i've still had less john mcvie quality bass tones come out of that DI though, so it's obviously just one ingredient in the magic potion.
glenn