*Unfortunately, I do not have too much that I can point to in reliable sources.  From what I know, the Sato stuff is probably correct.  Before he came to SOA, Irimajiri was brought into SOJ as executive VP specifically to focus on the consumer business because Nakayama's expertise was in the arcades.  I believe I read in an article that this is the reason he initiated the Dreamcast project from the US: he still saw himself as the consumer point man.  I will have to check my files on that to be sure.  When I interviewed Bernie Stolar, he claimed Irimajiri initiated the project because of a lack of faith in Sato.  My work is not published yet, so that can't be used in Wikipedia, but I just throw it out there as something that confirms some of what your other sources claim. 

 :As for ending Dreamcast, when I interviewed Stolar and Kalinske, they both pointed to Okawa as the main actor in getting Sega out of hardware.  This makes sense, as I have interviewed every American SOA president from Bruce Lowry to Bernie Stolar, and Stolar is the only one that indicated Okawa took an active role in the company's affairs despite being the chairman of SOJ from 1984 until his death (and briefly president after Irimajiri).  I think that both Nakayama and Irimajiri were both interested in keeping Sega in console hardware, but in the face of increasing losses Okawa, a software guy himself as head of a computer services company, and the Sega board members representing Sega's bank joined forces to oust them both in turn and then end the hardware business.  That is certainly the angle I plan to focus on in my own work, but, again, it's not published yet and I am still getting my sources in order on some of those points.  I know that's not much concrete info, but I hope it at least helps focus your efforts. 

 P.S. Sorry about my negligence on the SMS review; I hit an incredibly busy patch.  I will try to finish my review this week.