If you can't get the control over the 'look' you want using Particles, try experimenting with moire animation.
Make a piece of 2D art showing the thin linear or arced paths you want these sparks to take on a plane, with the lines getting thinner as the sparks would fade: start with white lines on a transparent .png or .tif BG.
Put that on the top layer of a Plasma Standard. For the bottom layer, make another similar piece of art, but with short thin lines perpendicular to the first piece. Animate this layer against the static upper layer using Alpha/Multiply/Alpha layer blending.
When you have something that starts to work, you can refine it further using UV warping, variable transparency and animating brightness and opacity.
Then, once you have one plane of sparks that works for you, duplicate and offset it in space and timing for density and dimensionality.