Desk top speakers at low cost

Have you considered a headphone system?  An AudioQuest USB DAC/headphone amp is affordable and sounds amazing with every model of Focal, Fostex, and Sennheiser headphones I've listened through.  You'll get more bang for buck and can put it all in the drawer when you're done or take it all with you.  

But to answer your question, I've honestly never heard affordable speakers that sounded good except DIY home built speakers.  If you're willing to build the speakers yourself then you can get both good sounding and affordable.  I feel that the closer I get to the speakers the easier it is to hear that they are cheap.  By building them yourself you are cutting out a lot of hungry mouths such as the speaker builder, the parent corporation, the distributer, the showroom overhead and the sales person and they will be affordable.

Best of luck to you!

If you have not tried RAAL SR1a 'earphones' then it is worh trying out. I hate headphones and these are like 2 channel sound. On sale in November.

True Ribbon Headphones & Amplifiers | RAAL-requisite (raalrequisite.com)

BTW - putting speakers on a desk is a difficult thing to do. Since it is not an ideal locaction I would consider the AudioEngine line of desktop speakers with the angled stands. No need to spend to much money on something that will really never sound great. 

Audioengine (audioengineusa.com)

I think some here have overlooked the fact that the OP has an amp and preamp and no need for powered speakers. You might consider the passive version of the Kanto line called the YU Passive 4" or the 5.25".

Their active speakers have gotten some really good reviews and I considered getting them unitl I came across a great deal on something else.

All the best,

Nonoise

Fluance ai 41 active speakers. $249/pair, 35 Hz - 20 kHz

+1 Fluance or AudioEngine ... price, sound and connectivity cannot be beaten!!

(I own Fluance)