Does the Creek have an HT Bypass function? If so, that is what will do this for you.
I'm not familiar with how an HT Bypass works, but you can do what you want by getting a home theater receiver with preamp outputs. Then hook the preamp outs for the L&R mains on the receiver into a line input on the Creek. Hook your center and surround speakers to the receiver as you normally would. When you set up the receiver's multi-channel balance, set the volume control on the Creek to 12:00 (or some other easy-to-remember setting). When you want to watch a movie, just switch the Creek to whatever line input the receiver is hooked to, turn the volume on the Creek to 12:00, and you're set.
Minkwelder is almost correct with one caveat. You need to trim channels levels on the receiver (using an SPL meter), based on the volume setting on the line input on the Creek. if a 12:00 setting represents say -20 db, you would have to offset by adding 20 db on the SSP which may be out of range. You will probably need to find something closer to unity gain on the Creek. However since you have no step attenuation with a volume level readout display, you need to set it at a high level (say 3:00) and possibly mark the correct volume level setting for HT mode with a piece of tape.
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.
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:
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.
The only issue with that approach is that "mid level" may be too much attenuation. If 12 O'clock is say -20db, then you would have to crank up the mains by 20db on the SSP channel trim settings, which may be out of range. If you take your approach setting the creek at 3 o'clock is probably closer to the unity gain mark.