The support team said that the chance to consider asterisk 1.6 or 1.8 is very low as they have concentrated effort to trim down 1.4 and fine tuned its in embedded environment. They considered 1.6 or 1.8 just add too many non PBX core features and not necessary for the design purpose of embedded ippbx.
Does your IP01 arrive? The two boxes I test encountered problem in SIP connection and audio problem. Both are sit behind a draytek router. However, IAX connection works flawlessly and SIP connection within Lan works.
My IP01 is sitting behind Draytek router but I don't have such problem as other C-Hings are facing. For one way audio connection with SPA3000, please check the ATA as per following.