For me, I caved and used the DLC.
Alm (Conqueror w/ Falchion)
Celica (Rigain w/ Mage Ring)
Delthea (Enchatress w/ Mage Ring)
Tatiana (Exemplar w/ Dracoshield)
Zeke (Skogul w/ Gradivus)
Mathilda (Skogul w/ Gradivus)
Lukas (Spartan w/ Blessed Lance)
Faye (Saint w/ Dracoshield)
Gray (Yasha w/ Brave Sword)
Tobin (Oliphantier w/ Killer Bow)
Before using the DLC and was having some issues with the tougher enemies beyond B5, but I did held well until I reached the dungeon boss where I couldn't really handle the reinforcements coming in. Then I just decided to use the DLC classes and pretty much relied on Tobin to deal some damage and using Faye's rescue shenanigans until I had Alm come in for the final blow. Meanwhile I had my other units camping around where reinforcements would come in to deal with them quick. Although some day I would like to try again and try to beat the dungeon without resorting to the DLCs.