I've got 3 male Chi's, two are 2 years old and neutered & one is 6 months old & intact. The 2 older ones are great friends & get along wonderfully. Sometimes the 6mo (Marley) will grumble at his brother (Maxie - they share dads) when he's sleeping & Maxie comes over for a snuggle...and vice versa. I correct it every time it happens. It has never gotten nasty or anything & they do play like crazy & 99.9% of the time get along wonderfully. My 6mo is just going through the adolescent phase right now & testing his boundaries & dominance.
Personally...I feel 2 (neutered) males would get along GREAT. I'd probably recommend that over 2 Females, IMO are more indepedent & opinionated while males are more laid back. Saying that, a male/female pair would work fine too because the males are so laid back & let the females do whatever they want. LOL Our 2 females get along fine but don't play together as often as they do our males. If it was just them it may be a bit different but both Marley & Maxie keep the girls busy themselves. haha
However, I most importantly feel that as long as you are a great pack leader...you can have as many pups, any sexes you want & not have any issues.