...What I may have missed is the need to create a custom paper using the HP solution centre. The problem I have with this is that the Hahnemuehle setup guide says that the paper type should be specified as HP Advanced Photo Paper High Gloss. However, no such option exists when I try to create a custom paper in the HP Solution Centre. The options they give for Paper Category are: Photo, Coated inkjet, Photo rag, Watercolour, Canvas etc. Any ideas about which one I should use?
I guess that you must have downloaded unzipped and installed the profile from http://www.hahnemuehle.com/site/us/472/hewlett-packard.html
as it shows in Lightroom?
I use the same printer but am unable to test due to it being out of action. But I downloaded the profile and installed. As this is a photo paper the categrory should be Photo for good measure I used both the Add Custom Paper and Install New ICC Profile
When you get to the Printer set up dialogue you should be able to locate the Fine Art pearl profile - in my case at the bottom of the window after scrolling
Had a look at your jpeg via LR soft proofing and can see the 'posterisation' using this profile is farily pronounced and switching to another profile e.g. HP Advanced Glossy, HP Advanced Photo Satin, or virtually any other looks better. It also looks better (at least on screen!) using Relative Colorimetric. So I wonder if this is really the correct paper choice for this particular image.
Hope that this helps you get a better result and also hope that you do not mind me making a couple of comments (which may or may not be relevant to the current issue
When I first saw the posterisation I wondered if it was possible that this could be related to a poor monitor profile (but why only in soft proof?). You said that you use the Spyder 2 for calibration and profiling I also have this model using SpectraView software rather than the Datacolor app. What I am aware of is this version of Spyder is not suitable for wide gamut calibration and could cause problems. Probably not the case however but worth a mention?
I noticed in the LR Print dialogue that you have set the Print resolution to 360 ppi. This would seem to be a multiplier used by Epson printers e.g. 360/720/1440. The HP printers similar to Canon use 300/600/1200. I think that the general recommendation is to use multiples of your printers native resolution and therefore it might be a better idea to use either 300 or 600 ppi. TBH I doubt that it will make a noticeable difference with this particular image.
EDIT: FWIW screen grab showing comparison in softproof Fine Art Pearl and Hahnemuele Smooth Fine Art, Perceptual rendering