Question followed by answers.
The thought of trying to run Dungeons & Dragons - or any other roleplaying game - with as many as 6 or 7 players seems like too many to me. I know some people who run big groups, I can't. It gets too boring for people waiting for their turn.
Amber Diceless, however, is entirely different. 8 players is a great number for that game. This is mostly because Amber players tend to talk in-character and scheme among themselves in little groups, leaving you - the GM - to run only a few characters at a time through one thing or another. (They can do this because they're not rolling dice all the time, and don't need you to come to decisions.) Most of the game happens in strange little parcels, anyway, with nobody but the GM getting the whole picture. Many players facilitates this best. In fact, we usually have to use several different rooms to play Amber, with all the activity going on.
If you have too few players, then these groups and cabals and secret meetings don't happen, and that takes away the strength of the game. It also means a lot more work for you, the GM, because then the players feel they are in a single group and must be directed. That is nonsense, and not the way to play Amber - there are other systems that will do that style of play better.
I wouldn't run Amber with *fewer* than five players, and even then I'd put some NPCs in the character creation auction. I'd even haul in friends who aren't playing to represent those NPCs in the auction, and I can take over the duties of managing them after the auction, just so that a social structure in the world is created. (This can be dangerous because guests can bid unaccountably, so make sure you get trustworthy people.)
//Panjumanju
I have run for two to three players at a time and it is fuckin wonderful.
First I have a group of NPC youngers so the auction is also against them. So getting first place or it being a secret still works. I also tell the player if I say your 2nd rank there may be other people within a few points I would tell the same. Until you have a clear contest with them you can have two people ranked the same but have different points in the stat. But I also always keep the points and don't use ranks Per se. So if you bid 50 points and got first and someone else bid 20 points and got second, you will always clearly dominate the other guy rather than be 1st and second rank.
The best thing about having a small group is how focused you can be on each one and how much more important the NPC's become. A little more reliance, give and take with the NPC's makes for an interesting game since you seldom , as a player, have even OOC knowledge of what that NPC wants or can do, or is doing. Makes it a little more mysterious.
But that is just my take on it.
I think that ADRP works just fine for smaller groups. The auction is best with larger groups, but actual game play can be done with many or few players.
I myself don't think I'd ever run Amber (or LoO) with anything less than 4 players at an absolute minimum. Even then, I'd rather have a lot more than that.