Hey there! First off, love this - just having the issue that sparring sounds were driving me crazy.
When I searched for a solution I didn't find much besides removing all battle music, but a reddit post revealed a solution: replace the standard battle sounds for the precise cases where a dwarf is fighting another dwarf with a blank sound reference. With a little alteration I managed to mute sparring, without affecting other battle sounds:
Add the following to Soundsense\packs\battle\battle.xml
<!--
Sparring Sounds Begin
-->
<sound logPattern="The (speardwarf|Spearmaster|hammerdwarf|Hammer Lord|axedwarf|Axe Lord|wrestler|militia commander|militia captain|captain of the guard|macedwarf|Mace Lord|swordsdwarf|Swordmaster|marksdwarf) (attacks|bashes|hacks|stabs|strikes at|collides with|charges at|misses|attacks|kicks|bashes|slashes|looks surprised by the ferocity of|scratches|bites|punches|strikes|strikes at|slaps) (T|t)he (speardwarf|Spearmaster|hammerdwarf|Hammer Lord|axedwarf|Axe Lord|wrestler|militia commander|militia captain|captain of the guard|macedwarf|Mace Lord|swordsdwarf|Swordmaster|marksdwarf).+" concurency="0" timeout="500" playbackThreshhold="5" ansiFormat ="[35;1m">
<soundFile fileName="" />
</sound>
<sound logPattern="The (speardwarf|Spearmaster|hammerdwarf|Hammer Lord|axedwarf|Axe Lord|wrestler|militia commander|militia captain|captain of the guard|macedwarf|Mace Lord|swordsdwarf|Swordmaster|marksdwarf) (is knocked over|stands up|is no longer stunned|jumps away|bounces backward).+" concurency="0" timeout="500" playbackThreshhold="5" ansiFormat ="[30m">
<soundFile fileName="" />
</sound>
<sound logPattern="They tangle together and (fall over|tumble forward).+" concurency="0" timeout="500" playbackThreshhold="5" ansiFormat ="[30m">
<soundFile fileName="" />
</sound>
<!--
Sparring Sounds End
-->
Put it directly below the line
<?xml version="1.1" encoding="UTF-8"?>
<sounds>
If you put it at the end, it won't catch all the sparring sounds (other sounds will trigger before the blank reference).
Credit to the redditor in question, /u/ianjosephfischer who posted the idea here:
https://www.reddit.com/r/dwarffortress/comments/4lobqh/soundsense_sparring_sounds_off/