hooked up TT and preamp to receiver sound fades out after 4-5 seconds

Connect the phono amp output into a different input on the receiver. 

Exactly! noromance is correct, once you purchased a external phono pre amp you need to use one of the normal line level inputs like...CD or AUX or Tuner or just about any input will work as long as its not the internal phono. 

The OP states that he tried hooking it up to the CD input, but the same thing happens.

I looked at that receiver.  My lord does that have a bunch of crap on it.  Most AV receivers need to be set up right from the beginning to work with non surround/video sources.

IMHO, there is something in the receiver's vast menu, not set up correctly.

From the manual.  This might be why your TT  didn't work plugged into the phono input the first time, (before you got the outboard phono stage).

  PHONO/LINE Setup • Default setting: PHONO You can choose whether you want to use the PHONO jack on the rear of the receiver to connect a turntable, or a line level component (such as a CD or DVD player).

1 Select ‘PHONO/LINE Setup’ from the System Setup menu. The current setting is highlighted in the display.

 2 Select either PHONO or LINE.

 • PHONO – High level setting for turntables (without a built-in equalizer or pre-amplifier)
 • LINE – Line level setting for all audio components other than a turntable (except those with a built-in phono equalizer

 3 When you’re finished, select ‘Exit’. You will return to the System Setup menu.

@mofimadness That's what makes this board great. Amidst the sturm und drang and other noise, these thoughtful, methodical solutions and thoughts still surface.