I'd like to write directly to InfluxDB and log with grafana.

I think the format should look like (in InfluxDB line format):

measurement_name XXXX123_ch1_aws=1234.0,XXXX123_ch2_aws=345.0 123456789000000000
measurement_name XXXX789_ch1_aws=1.0,XXXX789_ch2_aws=2.0 123456789000000000

That is, each channel reading should be a field, named for the serial number and channel. (note that since the timestamps and measurement name + tags match, this is a single measurement with 4 fields... i just split it for readability).

An alternative would be

measurement_name,serial=XXXX123 ch1_aws=1234.0,ch2_aws=345.0 123456789000000000
measurement_name,serial=XXXX789 ch1_aws=1.0,ch2_aws=2.0 123456789000000000

which is two separate series. I don't think this is as valuable because there's no reason you'd want to query for all the ch1_aws values across tags.

Another alternative would be

measurement_name,serial=XXXX123,id=ch1_aws value=1234.0 123456789000000000
measurement_name,serial=XXXX123,id=ch2_aws value=345.0 123456789000000000
measurement_name,serial=XXXX789,id=ch1_aws value=1.0 123456789000000000
measurement_name,serial=XXXX789,id=ch2_aws value=2.0 123456789000000000

The problem with this format is that each channel is a separate series, so you can't do interesting things like add two values together. For example, the plugs in my kitchen are on 3 different branch circuits, so I'd like to have a "Kitchen" value that is mean("ch1_aws") + mean("ch2_aws") + mean("ch3_aws") but you can't do that. This is possible with the proposed format above, though.