If you want to stay with quad then you only have 2 options if you want new....that is the qc24 (valve) or 99pre (no valve). I would tend to stay with similar ranges...match a 6 series pre with 6 series power for e.g.
Although quad power amps are well regarded, there are (or would appear to be from reading reviews and other forum posts) a significant number of people who think their pre amps are a bit of a weak link. The general opinion is that there is better out there for the same money. I am not in a position to be able to recommend anything specific at the moment. I live in a hifi backwater and anything even remotely esoteric (no not the brand name) is unavailable.
Another option, mentioned here a lot recently is a passive pre....adds nothing and takes nothing away.....I'm using one at the mo. Plenty of options there...from the 250 - 300 Creek or Icon Audio all the way up to infinity for some really delicious bits of kit. Have a look at Music First and you will see what I mean.
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