I'm not really sure what you're asking for here. If the Stolen Land 6-player conversion worked for you, then the RRR conversion should work about as well?
Don't raise the Hit Dice.
Instead, maximize the HP of every monster, and boost their numbers by 50%.
For single-large-creature encounters add the Advanced simple template, or another +1-2 CR template.
That should keep things challenging for your players without making the enemy saves and DCs so high that they steamroll the party.
For big important fights that will probably work well.
However, your players might get grumpy if the enemies have access to abilities that they can't get.
If they are all on board, go for it.
The conversion worked fine in some points, in others was still too easy and in a rare case too difficult.
Well, it's hard to say much without knowing which encounters they struggled with and which they stomped.
I always give solo and/or important foes max HP. Otherwise they go down too quickly for my tastes. And note that most creatures in the conversions already have the Advanced template, as it's the easiest way to bump up a monster's CR by 1.
I guess one bit of advice I would offer for RRR is that a lot of the opponents (maybe even all of them?) have no meaningful ranged combat option. So if a group can tie down the opposition and hit from a distance, they will have an easy time of things. In some areas this may not be possible, like the dungeons, because of lack of room or LOS or what have you. But in the open outdoors it's a different story. When my group attacked the lizardfolk I realized the lizardfolk either had to cower in their village and take it, or come out to meet the party and get hit while they closed the distance. I had given them a druid ahead of time, which gave them more options, but by the book they would have been screwed.
I would suggest not using single boss fight encounters. I would up the CR, by adding more minions that compliment the BBEG's. Kingmaker is already easy enough. As an example there is a hex with a dire tiger in it. Give the dire tiger some tiger buddies, or give it a humanoid companion(s). Maybe it is not eating them because they raised it from birth.
They fought the kobold chieftain? That's unusual, I would love to hear that story. Or do you mean the kobold sorcerer, Tartuk?
I agree with adding more foes when you can get away with it. If you have 1 opponent and 6 PCs, that's 1 round of actions you get to take vs. 6 for the players. Which usually works out very poorly for the opponent, unless they have some mass save or die/incapacitate effect. Given that your group is using 20-pt-buy, you might want to use the 6-player conversion and add in some extra foes. Personally I recommend giving some spell support to the lizardfolk and the trolls.
I've used (still using) the 6 player conversion for KM2-6 (currently starting 6):
- KM2 (5 PCs) - I run as is, but it was mostly very easy for the players.
- KM3 (5 PCs, 1 cohort) - Run mostly as is; only increasing HP to max and grouping fights near the end in V's Tomb as i saw they are having to easy a time. The fight with V was the toughest they had up to that moment.
- KM4-5 (4 PCs, 2 cohorts) - All enemies got a max HP. Important NPC enemies got a boost of 1-3 levels, or advanced template, etc.. Was a bit more challenging for most fights, but party was never in any real danger.
Final battle in KM5 was the toughest they had so far, lasted long and depleted most of their resources with several of the PCs/NPCs almost dying. The ECL for that last encounter was 19! The party was level 13 (with two 11th level cohorts).
- KM6 - first session tomorrow. I've already re-worked all encoutners from the 6 player conversion: Advanced Templates, more HDs, more monsters, more class-levels, etc...
I've also slowed down their level progression. So they are starting KM6 at level 14 and will only advance to 15 near the end (I don't use XP, so they level up when i tell them to..)
Part of what skews this is the amount of Wealth they have (apart from being good tactical thinkers and experience players). Lots of money and time to Create Items/Armor/Weapons/etc...
[EDIT]: by the way, while i used the 5 Player Conversion, since they were only 4 PCs i gave them the treasures according to the KM modules.
Hope that helps,
-arnon
I'll reiterate, because it's important-
Don't Raise Hit Dice.
The amount of hit points you need to give a monster to compensate for additional players is about 5 per level of the PCs. Getting those necessary extra hit points by increasing a reader's Hit Dice means adding an awful lot of Hit Dicey the time you get to the CR 5+ range.
Hit Dice give monsters extra Feats, Skill points, Saving Throws, and ability DCs.
Basically, if you add Hit Dice, your monsters will always make their saves, and your players will always fail theirs. It makes the game into a very one-sided game of rocket tag.
Instead, keep the Hit Dice where they are and add extra monsters, or add templates to them. Or both.
Frankly, I have no problem with the extras gained by HD. My party can deal with it, in fact, they'll steamroll over all but the most difficult encounters.
I don't throw many encounters at my PCs (no random encounters, and leaving irrelevant encounters out of the fray), so if the monster they meet do hit harder and are tougher (saving throws, hp) all the better (skills are irrelevant for encounter monsters). And no, they don't always save, and the PCs don't always fail; all it means is that the fights might take a round or two longer
YMMV... i'm fitting these encounters for my part of course.
Cheers,
-arnon
Adding a couple of HD to a monster isn't going to dramatically alter their power level. Getting maybe +1 to saving throws certainly doesn't translate into always making saves. Heck, the Advanced template adds +2 to everything (and +2 more to AC and CMD) and isn't a game breaker by any means.