Agreed, iTunes 10.5.1 update did NOT fix the problem for my HP MediaSmart (WHS v1).
Here are my test machines:
17" MacBook Pro running Lion with iTunes 10.5.1 ~ Does NOT work.
13" MacBook running Snow Leopard with iunes 10.4.1 ~ Works perfectly.
Dell Laptop running 32bit Win 7 and iTunes 10.5.1 ~ Does NOT work.
Gateway Netbook running 64bit Win7 and iTunes 10.4.1 ~ Works perfectly.
Clearly the issues is with iTunes 10.5(x) as 10.4(x) works perfectly on both OS/X and Win7 while 10.5 does not, even after the .1 patch.
In my configuration I have mapped the Music share on the WHS to iTunes on the MacBook Pro whcih is where I "manage" everything from. The other 3 iTunes installations don't have their own libraries at all, they have only been used to stream off the WHS iTunes share.
I was seriously considering iTunes Match and was waiting for the 10.5.1 patch to fix this problem as they have done in the past when they broke ths same functionality. I'm not holding my breath, but I have decided to hold off any further considertion of iTunes Match to see if Apple is going to handle this satisfactorily or not.
In the mean time I got a Google Music account which easily uploaded my entire iTunes library (though it did take 2 days to do so) and at the cost of FREE is quite a bit cheaper than iTunes Match anyway. Using Google Music I can stream my library to pretty much anything that has a web browser. It even works in the background on my iPad. With this, I'm not even sure I care aboout the iTunes server any longer. Oloy real drawback is that Google Music requires Internet while the iTunes server could stream on my local LAN even if the Internet was down. Might also be a concern if you don't have unlimited bandwidth.
