Bit annoyed even at the discounted rate... Don't where the software is or how to get is working!?
 
Any ideas team?

I would say I have not downloaded a pack but have downloaded other software.
First there is a place in the browser or when you download as to where you download programs to (a folder - mine is called Downloads).
That is where it is.
 

Right in an effort to make sure I remember to post solutions (that worked for me), here we go:
 

 
This fix sorted my DLC and made it visible and usable in Sound Center

Oh my link was removed... so try searching on:
 
"Are you an existing MC6T user and your new DLC is not showing up?"
 
On the Steam Music Creator 6 Touch General Discussions on the Steam Forum.
 

Always look at the destination selected for the DL.... I made that mistake so many times it isn't funny. It will generally be in the DOWNLOADS folder or the TEMP INTERNET folder (by my experience).
 
In the rush to get to the new toys, we tend to overlook that destination thing. Send it to the desk top is the easiest way.

first - I don't understand what "Steam" is?
 
2nd - the reason your link was removed is because you have less than 25 posts.  that's an anti-spam feature of the board.
 
3rd - if you have win7 or win8, then as Herb says, your download will be in the DOWNLOADS folder UNLESS you're using a download manager other than IE.  if you are using a 3rd party download manager, then you'll have to figure out from it where it defaults the downloads.

Steam is the client from http://steampowered.com - get with it daddio!

Do a Search for it by Start -> Seach - even a partial name will bring up anything that resembles a program or download or folder.
Otherwise there is folder Programs (x86)->Steam->SteamApps->Downloading perhaps or looking through Explorer on your computer also to find anything.