You make some good points, but let me point out a few things:
I have tried to steer away from splashing a few squated Monk and Paladins levels. I don't like doing this because it feels wrong to me. These classes are supposed to be used in conjuction with one other, hence their orders - not part of a multi class build (Case in point Paladin/Sorc, considering you can be a pal/wizard, but not Pal/Sorc it seems pretty obvious that these classes were not intended to be able to be played together, while a Monk of the Dark Moon can be a Monk/Sorc. just fine). While strictly speaking these might add power to a character, they feel like cheating to me, a bit like getting HoF items in normal mode. This is a personal thing, others may not agree but I prefer using multiclass builds that have no restrictions.
A note on the party:
1. Asamiir or Female Drow Paladin of Illmater:
I really don't see a reason for 15 Pal levels! More cleric levels and a few monk levels and / or fighter levels would be more effective!
Especially as the pal levels are more or less redundant to the cleric levels!
I look at this in reverse, how many Cleric levels does he need? What real advantage is there in taking more than 15? He is not the party's main cleric, 15 levels gives him everything he needs in the way of spells. Remember that this guy is primarily a tank. His Cleric levels come later. More Pal. levels give him more Hp, better BaB and a stronger Smite Evil while still being able to Holy Word and Heal himself.
2. Human Fighter5/Rogue5/Barbarian20:
a build with no caster levels shouldn't be real effective in HOF - ok he has tons of HP but can't reach any useful AC, can't use the bands for more DR (as they should be monk only AFAIR) and against the tougher ones of the HOF enemies you will need to cast heal or ressurect spells on him every 2nd round!
Even worse this guy has no SR (and no chance to get an effective one) and has worse will saves!
As you ahve pointed out previously, AC is essentially an all or nothing in HoF. In HoF he's going to get hit all the time, this is where DR comes in handy, Barb's are the only class with built in damage resistance that stacks, and yes he can use Bands of Mastery, they are universal. His High Hp will keep him alive for a while, even against slayer knights. He's also the perfect carrier for a Greater Shield of Lathander from the Cleric. He can also Greater Rage at will for +90 HP (at 30th level) if he's taking a beating, which should give you the few moments necessary to Heal Him. Particularly if he's in the front line with the Pal. From my expericence Mirror Images are great as long as you have about 10 caster levels, with 5 or so levels you normally get about 3-5 images, which disappear in a matter of seconds. You also need to combine this with the ability to recast MI multiple times, and/or aviod getting hit (either with Blink, Blur etc. or Huge AC).
Also, sure no SR, but does have Evasion against area damage spells, and Rogue levels boost his reflex save.
3. Human Bard17/Fighter6/Rogue7
ok - this one has a better potection but 3 rogue and 4 fighter levels would allow you 6 additional levels for barb 3 and ranger 3 or bard 20 - would be more "ultimate" this way
20 Bard levels is pretty pointless IMHO. You still only have 6th level spells (even if you had 7th they suck), though you would get more castings. Fighter6/Rogue7 gives you more feats than other builds (except perhaps for Ranger levels for the Dual weild feats) and a great sneak attack. Don't underestimate sneak attack. This is how he will do most of his damage, as he will almost never be the first into a fight, he will usually be flanking his opponent. The extra Rogue levels mean his first hit at each opponent does and extra 4-24 damage, basically turning a normal attack into a critical hit. His fighter levels give him enough feats to take 2 weapon fighting, weapon spec. and max. attacks ontop of his magic related feats. Considering he can cast Invisibilty so that he gets to sneak attack again once he attracts attention, all those extra 4-24's add up!
5. Human, Wild Elf or Asamiir Sorceror:
as the aasimar pal 2 / sorc X is plainly *the* ultimate build...
Don't like doing this for the reasons above. These classes were not intended to be played together, so I don't. In any case, Monk levels give you improved evasion so you will take either 50% or no damage against area damage spells (instead of a definite 50% with high saves) and a bunch of other nice feats including a will save bonus (already high from being a Sorc. and boosted by being a Monk also, even with 10 Wis and no boosting feats this would mean a will save bonus of +21) against mind affecting spells.
Yes, I've played a party like this through HoF. Basically nothing survives 4 simultaneous castings of Symbol: Hoplessness at a time, particularly if they've been Emotion: Despair'd by the Bard first. If something does, by some miracle save 4 times, Holy Word stuns it for a round with no save and no SR while the Pal, Barb and Bard all take a round of free shots at it (with the Barb and Bard getting their Sneak attacks!).
It's also a very robust normal mode party. Constructs are a bit of a pain as they are immune to Symbol and Greater Command, but since Hof gives you the Kegsplitter it's no biggie.
What difficulty did you play on in Normal Mode? Your party looks pretty tough, and you didn't die very often I have to say. To be honest there are many ways to build a powerful party. In General, any party with at least one Cleric and either a Wizard or Sorc able to cast level 9 spells with the right stats, a utility character and a tank will probably do fine.