Yup when I bought my MP3 dealer talked to Ralph who said resistor package really not worth the $$$.To be clear on this, what I tell people when they ask is as @pstores described- this is one of our more expensive options and offers the least 'bang for the buck'. But if you are going for the nth degree in resolution then they should be considered. @clio09 is also correct- Caddock makes these custom for us.
Being an audiophile in the old days I would change out all sorts of parts in the quest for better sound. That is why we have the options. We've found over the years that if people try to make part changes in our gear, more often than not the equipment winds up being a mess inside- often too with compromised performance. So if you're wanting to push things as far as they can be taken, we've already auditioned the Caddock (and other) parts, we've checked their specs, we've tested them to see how they hold up. So we can build them in and keep things looking nice inside.