Since the end of the season, we've lost Sinclair, Garbutt, Graham, Kashi, Nelson (presumably), Mousinho (not in regular first team plans), and Browne (and others fell by the wayside who were not first team regulars). Let's not talk about Eastwood and Whyte - hopefully neither of those will be heading off! On the plus side, Hall and Baptise *should* be ready relatively quickly. So I reckon that's 7 gone and 2 back in contention.
So six new signings doesn't seem unreasonable IF they are proper first team players rather than development players. You'd also suspect the club are counting on one or two of the current U23s playing more of a part next season.
That does of course beg the question - how many of the new signings will be proper signings and how many loans of young inexperienced players from up the pyramid that might or might not prove effective? Of course if Whyte and/or Easty end up being sold, then those two will have to be in addition to the six - not included in them!