incorporate 2 channel amp into multichannel system

Yep, Edorr is correct. My bad for attempting a quickie response. The 12:00 setting has worked for me with my Yamaha receiver and the three different active preamps I have used in my 2-channel setup. The Creek is a much different animal. Not only does its preamp have a passive stage, but it also has three selectable gain stages. The actual volume control setting on the Creek will depend on several variables, including the output level from the receiver's preamp. A higher volume control setting on the Creek may be necessary to remain within the receiver's range.

Gentlemen:

What you have described is the procedure for emulating a HT Bypass when that function is not provided. It is an input on the 2 channel preamp with an accurately fixed gain into which one feeds the L/R line level outputs from the HT or MCH processor. Then, setup for each is handled independently but the L/R signals are always routed through the stereo preamp.

I use a Parasound JC-2 BP for this and it is fed with the L/R outputs of my Meridian 861 as well as directly with analog stereo sources. Related stories here:
http://www.stereophile.com/content/music-round-47-page-3
http://www.stereophile.com/content/music-round-34-page-2

So for example if I connect a cd player to the creek I can determine with a spl meter where 0db is and then mark it as my ht volume. Is that correct?

No. First you need to get a multi channel setup disc. Next you play it in multi channel player connected to your SSP. Then you calibrate your channels individually, using the channel trim feature on your SSP. You could do this by setting your center and mains to 0db offset level on the SSP, and then find the volume setting on the creek that gives you the same SPL reading for the mains and the center. This may or may not be exact unity gain on the creek, but that does not really matter, as long as your 6 channels are calibrated correctly relative to each other.

That's one way. The simpler is to connect the L/R outputs of the SSP to the Creek, set the latter at a mid-level of the VC rotation and mark it so you can repeat that setting accurately. Then you run the SSP's setup/calibration for all channels via the SSP and the Creek. Done.