The Tome of Atanatar is arguably the most powerful of the four record attachments, because it has the best targets in being able to recycle Sneak Attack (with Gandalf) and Strength of Arms. This was my initial attempt to absolutely focus down that approach, with 3x Sneak, 3x Strength of Arms, 3x Tome, and 3x Second Breakfast to recycle Tome. With the addition of more recent cards like Reinforcements this whole approach gets bolstered even more.
Strength of Arms is kind of secondary to be honest, as powerful as it can be. The main point here is to recycle Sneak Attack Gandalf as often as possible, so you play it, you play it with Tome, and then you try and draw as fast as possible to get it back from the bottom of your deck so you can play it again (and then play it again with the Tome you retrieved with Second Breakfast and then draw and play it again). Or, you can use Send for Aid to pull an ally and crucially reshuffle your deck to hopefully bring it closer, or Gather Information to pull it from the bottom of your deck (and reshuffle afterwards if you Tomed multiple copies). Reinforcements gets you more Gandalfs, plus other players can chip in in multiplayer with their own allies. Finally Grave Cairn is pretty decent here, because if you Sneak Attack Gandalf this much, you may as well have him add his to someone else when he leaves, so it's like he's helping with combat as well as questing that round (or maybe he's helping twice because you Sneaked him a second time).
The sideboard is mostly a selection of out-of-sphere allies who also can be worth Sneak Attacking or Reinforcementing - Beorn for big hits, Elrond for his enters play effects just like Gandalf, Éomund in case someone's playing a Rohan deck, Landroval for those "a hero is about to die" emergencies, and Galadhrim Minstrel to dig out important events and reshuffle your deck after you Tome your Sneak Attacks to the bottom (or I guess in multiplayer you could use Reinforcements to send her cross-table and help someone find A Test of Will if you want to be a team player or something, w/e)