Can my router B618s output to 108.11/ac be attenuated?

No, unless the distance is to great in which case the signals attenuate.

This is High Quality original LINKSYS AC Adapter Charger

Input Voltage: 100V-240VAC (50-60Hz)
Output Voltage: 12v1a

Model: AD12V/1A-SW

DC Plus Dimension: 5.0mmX2.1mm

Compatible Models:

WAG300N

WRT54G

WRT54GS

WRT300N

Linksys Routers

A DI like this is so simple one doesn't need a manual. If you get buzzing or hum, try opposite setting of the Grd Lift switch. This switch breaks the ground connection of the XLR output connector to the case/shield. The attenuation switch allows you to vary the output from this for devices that generate different levels. Set the attenuator to 0 for low level devices and to the middle setting for mid level and use the -40 Db for high output devices. The two 1/4 inch jacks are in parallel so you can for instance run an instrument into one and back out to your amp and the XLR then goes to mixer for the house PA. Passive guitars you would usually use the 0 Db setting and keyboards often the mid setting or the-40 Db. One caution as I use these boxes... it is easy to leave the slide switches "between" settings and you will get no output.

Specs for this router says it draws 15 amps .
15 amps X 110v =1650 watts

I doubt that converter would last very long before going up in smoke

It Seems like it is an issue with the firmware

Click here to download the latest firmware

Yes, make sure you have a new power supply with the right voltage output, enough current (if the new power supply is rated for more current output, it will be OK), and the right plug with the right polarity.

Check your power supply, some will actually work with a wide range of voltage, some actually go from 100-250VAC. 50Hz-60Hz

Since you are able to view the output i'm assuming you are using an oscilloscope and only the positive or negative half of the sine wave is displayed. The output stage will be using a complimentry pair of output transistors, one amplifies the positve half cycle the other the negative. These are driven by a driver stage (phase splitter). One side is not amplifying. First measure the pos' and neg' LT supply rails. If ok check
ouput transistors with analog Ohm meter for base / emitter / collector continuity. If the amp uses an output IC and LT supplies are ok then use scope to view input signal, if input ok but output bad then IC is suspect. Since both channels are affected your problem is most likely a missing LT supply rail.

check mute or attenuation function

You have turned off your "POWER IC" option. This truns off the internal amplifier and only attenuates the output the the RCA terminals. That's why only your sub output works.

make sure your tape monitor switch is not on.