Ok, I've have soaked the seeds (50 sikkimensis and 54 velutina) in water I had boiled and then cooled previously, they have been in the water for 48 hours in a room at 24 C.
Now I poured hot water on some dry baby wipes, and when they had cooled down I packed the seeds in them and placed them in a plastic bag. I'll place them in a room at 25 C during the day and in another at 12 C during the night.
(Trying to follow the informations I found on this document: Seed Germination Studies in Musa. II. Alternating Temperature Requirement for the Germination of Musa balbisiana on JSTOR
""The temperature differentials optimal for germination in soil are dependent upon both the high and low temperatures, and range from 8-23 C. Germination is maximal when the seeds are held 6-12 hr at the high (27-35 C) and 12-18 hr at the low (12-18 C) temperatures. Some germination can be induced by short exposures to alternating temperatures followed by constant high temperatures, but continuous exposure to alternating temperatures is necessary for maximum germination.")
I hope I'll get something...