Should I use pre-amp

I have accuphase dp-700,going to my audio reasearch 600,to
my nearfield pipe dreams speakers,modifyed.Would a pre-amp
make any difference?
Sometimes a preamp will smooth things out . But if that isn't an issue , and you only have one source , I'd stay with what you have .

It is quite possible. If there is an ARC dealer near you I would ask to borrow their demo and compare. I have an ARC Ref 110 and have found that a preamp makes a huge difference in my system
Post removed 
Save your money. You have one source. By the time you have found the right cables and a preamp you will wish you never started.

Every preamp I have tried, gave with one hand and took away with the other.

If you have leading edge information and clarity to spare then maybe you will find a preamp that will work for you.

However you may be better off finding a DAC with switchable voltage on the output and volume control. There are a few out there, and I am sure over the coming months many more.
I run both my digital sources (Berkeley DAC and Esoteric X03SE) directly into my amps (after bypasing the preamp over a year ago) and have NEVER looked back. The improvement was staggering. I cannot possibly see how adding a preamp and cables between them and the amps would offer any improvement. I do use a preamp for my phonostage, FM tuner and hard disc recorder as I just can't switch cables for every source (and the FM and phono stage do not run the amps properly). I do switch cables to hear the dac or cd player or preamp and the inconvenience isn't a problem cause it sounds so darn good. I am not a believer of the term "no preamp is the best preamp".
thanks everone I'll just go direct