You don't often see Tyranids fighting Chaos, so this is a rare treat.
We played a 96AP game of HOTT last night, using my Epic 40K armies. Each army had four commanders, and troops were split up between them. On one side were (obviously) Tyranids, under Gary and Caesar, whilst Geoff and I used a Chaos army with a few Dark Eldar allies (because I don't quite have 96AP of Chaos troops yet).
Here's the setup. The table was 6' wide, but maintained the usual 2' depth for a 1" to 100p groundscale.
Some Chaos. So chaotic that Khorne and Slaanesh were fighting side by side.
The Chaos centre. The Demon Engine is the CinC.
The Chaos right flank was the first to see action, with it's war-engines and tanks piling into swarms of small Tyranid warriors.
More action in the centre saw Chaos Marines fighting various large Tyranid horrors.
On the right flank things started going badly for the forces of Chaos, as horrors swept out of the ruins destroying everything in their path.
However it wasn't enough - one Chaos Land-Raider kept pushing back its opponent which, in turn, kept pushing back the Tryanid's Dominatrix (the army's magician CinC). It was pushed back so far that it was shoved off the table and lost. This broke the Tyranid army, giving Chaos a rather fluky win.
With time in hand we carried on the battle. The Chaos right flank troops now tries to reorganise and roll up the Tyranid army.
On the other flank things had developed slowly, due to PIP starvation and the fact that neither side felt there was much advantage in pushing the attack.
The Chaos CinC was isolated by a swarm of Tyranid hordes ...
... and destroyed.
Gary finally attacked the Dark Eldar allies holding the left flank, with the Tyranid monsters more than equal to the task of defeating the lighter Eldar attack-craft.
The Eldar broke, and this actually broke the whole Chaos army in terms of losses. But it was, of course, only a hypothetical win.
The Tyranids very much had the better of this game, and lost it to some unfortunate positioning and unlucky rolls. But it was a fun game with tons of figures on the table and plenty of action.