Another option that would be super easy to use and adjust:

Run a fixed loop of amsteel through the channel (AHE sells these and calls them a "chainlink"). After running through the channel, tuck one end of the doubled over loop through the loop on the other side and cinch down. This locks the chainlink to the hammock. Then just attach a cinch buckle or a set of rings to the end of the loop w/ a simple larks head or prussic knot. From there you just need a polyester strap at each end of say 14' w/ a sewn loop at one end. To use you wrap the strap around the tree and connect the loop to the strap w/ a biner. The other end adjusts at the cinch buckle or rings.

In my opinion this is a very simple system w/ no knots in the field required and only minimally more weight than whoopie slings and less weight than your slap straps.

Here is a link to the gear that you can get to make the switch:

Arrowhead Equipment (chainlinks, straps w/ sewn loops, rings):

And here is a thread that describes the basics of a straps & rings suspension:

And if you want to use a cinch buckle instead of rings (IMO the buckles grip much better), here is a link to Onrope1:

Good luck!