AVR preamp out question

Depends on the AVR. Harman-Kardon preamp-outs wouldn't allow you to do this, for example.

Why? What are preamp-outputs good for if they will not output a signal?

I have a HK 7200 i use in 6 direct mode with the pre-outs to a forte 4a for 2 channel to merlin tsm and it works great-not sure what the problem would be.

Thanks for all your responses. I did try it again and it works. The problem was that my "little 5687 tubed linestage" doesn't have much output gain so that I have to crank it almost 3/4 full throttle to match my AVR. But it sounds great.
I just bought a Rogue Stereo 90 Magnum from a fellow A'goner and it sounds to good I had the "upgrade bug. I bought a pair of AZ Hologram II speaker cables, a Shunyata Aries IC, and a Cardas Clear USB cord for my Macbook/Maverick DAC !. My system is slowly evoving nicely.
Thanks again!

System:
Macbook/Maverick DAC 1 / Cardas Clear USB
5687 Tube Line stage designed and built by Randy Fay ($350 EBAY.)
Sony DA30ES 5.1 AVR
Rogue Stereo 90 Magnum
Silverline SR12's Front
NHT 3 Center Channel Speaker
AR 18b Speakers Rear
Energy 10 Subwoofer
AZ Hologram II Cable
Shunyata Aries IC''
Soundsilver Trilogy IC
Art Audio 1c IC
AP Copper Oval

Progress not perfection......