What power does it make in each wiring mode?

DS18 rates it at 70 watts RMS per channel into 4 ohms, 140 watts RMS into 2 ohms, and 220 watts RMS bridged into 4 ohms. Bridging pairs two channels, so you get two bridged outputs from four channels.

Will it fit behind a seat or in a small cavity?

It is built as an ultra-compact Class D amp, so the chassis is much smaller than a typical full-size four-channel. Measure your mounting spot and check the listed dimensions before buying.

Can I run a subwoofer off it?

Yes, by bridging two channels into a 4-ohm sub, which gives the highest rated output. A single bridged pair leaves the other two channels free for speakers, but total sub power stays modest.

Does it have built-in DSP or crossovers?

No. It is a straightforward amplifier without DSP processing, so tuning depends on your head unit and any separate processor you add.

What speakers pair well with it?

Efficient 4-ohm coaxial or component speakers suit it best, since per-channel power is limited. Avoid low-sensitivity speakers that need more wattage to get loud.

What comes in the box?

Expect the amplifier itself with its mounting hardware and basic installation fittings. Check the box contents for the specific wiring and fuse items included.