I'm having a similar issue right now, 1.6 (not 1.6b) with xecuter 2.3b pro, and M8+
Ive tried setting the lba48 options a million times (both as all on F and F/G), and it just won't work. When its set either of the above ways, it only sets the F to 129 gigs, and won't format G. If I put the hard drive in my other xbox, it shows the F being 242 gigs (its a 250gb HDD)
Its like evtool just wont accept my settings