P0420 trouble on 2000 Subaru Legacy GT

I have a 2000 Subaru Legacy GT with a recurring P0420 code. Work so far has replaced both O2 sensors and the cat (aftermarket model). Car seems to run fine and has no other codes.
There was a recall to reflash the ECM that was done a number of years ago, according to Subaru's records (before I got the car).

In trying to figure this out, I've noticed that two different scantools are not able to 'see' the front O2 sensor. Is this proper for this model? This makes it difficult to compare the sensor outputs of the two O2 sensors to see if there is a difference. That's how you determine if the cat is working, right? Is there something wrong with the ECM?

I think the car has the wide range type front O2 sensor as it has 6 wires, 4 of which are sensor signals. Is there a way to check it out independent of the ECM/OBDII?

How about an alternate way of checking the cat?

If you check the forums you'll see lots of testimony about less then stellar results with some aftermarket converters. As for your scan tool readings that seems odd that they won't read the front 02! Care to elaborate on which scan tools they are?

My scantool is a CarChip Pro from Davis Instruments.
My mechanic has a SnapOn model, not sure about the exact model number.

They both seem able to 'see' most all the other sensors.

Also, the cat is a model from Davico Mfg., a one piece unit with both cats and flanges that bolts right on. It seemed legit with a two year warrantee.

Well after much consternation, I decided to replace the cat with one that has more of the good stuff, supposedly. It has been a week and it seems to be working. Remember that I had replaced both O2 sensors along with the cat before. I have not been able to detect other problems that could kill the cat.

So how often do aftermarket cats fail soon after installation?