no idea sorry. if it was me id just try it from xmb, (had to say this because i did do it from xmb)
since its you , id advise you stay on rogero the extra stuff in rebug you probably wont use anyway. (i have to advise this cos i dont want you to hold me responsible if you brick) the order i would try is:
install rebug .999 downgrader from xmb.
then install toolbox2,
then toggle Qa
then install rebug 4.25rex
i'm not saying it willl work, im not saying its possible, i'm also not saying it wont brick your ps3. all i'm saying is thats how id try it, but i've got 2 ps3 and if one died id be upset but at least i'd still have a ps3.
doing it that way, even if you cant get to rebug 4.25rex the rebug 999 downgrade pup is identical in functions to the rebug3.55 rex other than it will report wrong version number.