Bummer. I lost contact with my TP-LINK WR941ND several times during my experiments, and always a 30 second reset was enough.
But you are able to get into redboot, thats good. I did that a while ago when I did my Fonera. It had an instruction on reset of the NVRAM from within Redboot. Probably/Maybe it also for you, though you may need to recalculate the exact hex memory position, and I am still not responsible.
Also, DD-WRT for the ECB-3500 is with activation, so I guess you paid for the activation, possibly you can expect a little help from them.
I selected TP-LINK myself. The WR941ND has the fast CPU speed and plenty memory like yours, but no activation needed, and not very expensive. I also have two WR740N’s. Dirt-cheap, and also 400MHz/32MB/8MB. But only v1/v2/v3 hardware can be put with DD-WRT, so buying them is a risk, you may get a V4. I agree they do not have the best radio’s, but I plan to use Ubiqity devices on the LAN ports anyway, the TP links local radio is for inside the house only,
—
Also, the first time I ran the setup command (on the FON2200, early experiment), it broke my device too. On second attempt, I manually took each of the commands that were in that command-string, analyzed the actual setup.sh after the wget, and found it referred to a network port that did not exist on atheros devices. So I manually tweaked the setup.sh before I ran it. (eth1 had to be replaced with ath0 or br0)
Since then, they actually fixed the script, its now compatible with atheros, but maybe you have something similar. Maybe your device does not have a br0, which would mean that when they fixed the script for atheros, they broke it for you…..