Hi Ricardo, and welcome
In a tank this size I´d say you could either keep a couple of one of the bi-parental Xenotilapia or a harem group of one of maternal Xenotilapia species.
The bi-parental Xeno´s like X. papilio and X. sp. "papilio sunflower" can be quite hard on each other and it’s not always easy to get a steady couple. This paper is dealing with X. papilio, but the info can generally be used on many of the other bi-parental species: http://www.cichlidae.info/article.php?id=359
Xenotilapia flavipinnis are also bi-parental, but not nearly as aggressive as the species in the papilio-group, and with a little luck and the right decoration, you may even be able to keep two couples.
I don’t think there’s enough room to house more than one male of one of the maternal species (like X. ochrogenys, X. sp. "ochrogenys ndole" and X. bathyphila) in the long term - eventually one male will dominate and harass the other(s). They will work much better in a harem group, consisting of a single male and several females. As long as there is some shelter for the females (rocks or a group of water-plants, like Vallisneria in one end of the tank), this should work out fine.
So, there´s actually several sand-dweller species that could fit your tank
All the best,