Yes Luke,
Both have L/R inputs and outputs, however, the are not the same type of units. I'll try to give a brief description of how they work.
The SM-26 is a splitter/mixer, so you can take two signals in, and split them into three stereo outs with independent level and pan control on each channel. You can also do the reverse, six mono channels in, mixed into a stereo out, with the same controls. You can also use it to mix six in, six out if you wanted to, with level and pan control to each channel. This is why it's known as the Swiss Army Knife of splitter/mixers.
That is the original SM-26 which has a brown face panel, and is hard-wired with an AC cord. The later model, the SM-26B, uses the wall wart power supply, and has a black face panel. this does all of the same things as the older model with one added feature. The SM-26B has jumpers in it you can change to split it 2 X 8, or 8 X 2. the upgrade will allow you to use the Master In/Master Out as level controls for these additional mixes, but with no Pan control.
The SM-82 is a 1U rack 8-Channel Mixer. You can use that to mix four stereo, (8 Mono), signals into a stereo, (2 CH), line out. This gives you Level and Pan control on each channel, with an Aux Send/Return to each channel. This would be good if you wanted to mix four ADA preamps into a stereo effects chain before your power amps. Unfortunately, you can't split like the SM-26, it only works this one way. You can also use the Aux loop to parallel your stereo effects in the signal chain, and run all four preamps into one stereo poweramp.
I hope this is helpful.
Harley