For me, the sr009 does not suffer from sibilance of the hd800 but it has a similar kind of non-attenuated mid-highs to upper treble. Some seem to have success with various amps to control the HD800. But I am unclear how that works out as the phone suffers from acoustic ringing right in the sibilance region (in the order of 3-4dB, what amp could possibly tame that and only that?).
Some may feel like the 009 is a bright headphone (or call it bass light / lacking body / foundations). This is more or less of an issue depending on listening preferences (music type / loudness level / preferred else accustomed voicing) and upstream gear ( amplification / source ...).
IMO, you can't have the cake and eat it, ultimate resolution comes at a cost: that of discovering the ugly part of some (hopefully a minority) of your recordings.
If you're not really after the ultimate in resolution / transparency / airyness, there are many other (possibly cheaper) options, including orthos.
On the sibilance, you're spot on. I have a couple of recordings that are sibilant. With the 800, I instinctively reach for the volume knob but today with the 009, I was able to listen to the song without wincing.
By the way, the 009 is not a bass light can at all,IMO. I have some Led Zep recordings that have a heavy bottom end and the 009 was very faithful to the source.