Hi,
as a long term Quad user, and currently owner of 2x606, 1x405 and 1x303 amp..... I am not exactly unbiased!
However.... I believe you bought yours used.... it might be worthwhile getting it checked out by Esmond, the Australian Dada representative (he currently is finishing work on one of my 606's)
It might be that you don't go for the Quad "house sound" - but it might also be that your 909 has had a hard life....
The 606's/707's are well nigh identical to the 909's - power supply is the main difference, and if you upgrade the 606/707 with dada you can eliminate that advantage...
Which leads me to an exercise I recently did - I purchased a 2nd 606 - compared it to my existing one - (sounded the same) - then sent it to Dada for the full upgrade....
I then compared them again - the upgraded unit has the same house sound.... but sweeter, smoother and firmer more dynamic....
I also have a brand new Onkyo TX-SR876 which is considered a reasonable quality Receiver/Amp..... but the Quads were definitely better - even without the upgrade.
In days of yore when I worked in "HiFi" I used to sell Quad alongside Revox, and a few of the more mainstream brands (Pioneer, Marantz, Dual....). The quad amps were then midrange kings - and good throughout the range.... I remember finding the Revox a bit too "clinical"/"Cold".
In any case I doubt you will have trouble finding a home for your 909 if ultimately it is not to your taste.... there are lots of us "Quad heads" out here.
Best of Luck
David