Am I damaging my Preamp?

All:

I have an analog preamp (Audio Refinement Pre5), and 3 sources (DVD player, Computer, and outboard DD decoder).

The DVD player is fixed output
The computer soundcard is variable (ie. volume control)
The decoder is also variable (ie. volume control)

I have the DVD player into the preamp, and it sounds great.

I have the two variable output devices hooked into the amp. The problem is that they sound a little thin, this way. However, when I pass them through the preamp, they sound warm and nice! Much preferred.

My question is, am I doing damage to the sensitive inputs of the preamp by doing this? I've been told to not ever plug a variable output into your preamp inputs: you’ll kill the pre by overloading it’s sensitive preamp inputs. Is it safe to do this if I keep the volume low on the source, and just use the pre-amp volume to listen to my music?

What I described above is really no different then the millions of people out there with their iPods and MP3 players, each with their own volume control for their headphones. But they basically go through the same thing I described, when they take their mini-headphone jack and output it to the input of their own receiver via L/R RCAs. Double-volume and all.

Thanks for any help!

Jason