bucketheadben,
I own the 6000D Coinmaster so the series Di 3 is a few after mine. Both are good machines, the Di3 uses larger/heavier batteries and as others have told you it gets heavy after swinging it for awhile. Whites may still offer a hip mount adapter set for it, this is likely a set of D rings on metal clips, a new upper end rod and armrest and possibly an extension for the cable. The metal clips will attach to the box by removing the existing screws, inserting the metal clips and reusing the original screws. Putting the box/meter on ones side really reduces the swinging weight and that makes the detectorists arm much happier. If Whites does not offer the kit ask them if another type of hipmount parts will fit the Di 3. By this I mean the upper end rod and armrest and possibly some D rings with the metal clips. Once you have these items one can construct the straps for the neck hanging/over the shoulder hip mount system. I believe the hipmount upper end rod and armrest for my XLT fits my 6000D.
I do not know how close the electronics/knobs are between the 6000D and the Di 3 however if they are close enough some special setup tips I purchased 'a long time ago' might apply. They allow one to super tune the unit so that one KNOWS what type of target is in the ground before one digs it up. This is handy but like I say I'm not sure if the instructions will work for the Di 3. I do not have the 6000D info at home so it will take me some time to get to them but if you want them send me your mailing address and I will eventually get you a copy to you.
The manual for the Di 3 is available on the Whites site under manuals. Down load it for free. Let your friend use this machine for 3 or 4 years before upgrading to a new machine, much of the experience will transfer to a newer machine though the learning curve for a newer type machine will be different than for the analog Di 3. And as you likely know, good earphones and diggers as well as good digging manners really help in detecting. In the summer the cup type earphones really cause one to sweat so if you can get ones with removeable/replaceable ear cups with or make some cloth covers this might help.
Good luck, have fun and may your friend have fun.
Regards, 63bkpkr