JD7

From Radial Engineering:

The JD7™ is a guitar signal splitter that is able to drive as many as seven amplifiers at the same time without introducing noise, signal loss, or hum and buzz from ground loops.

The JD7 allows you to feed up to seven amplifiers simultaneously, with premium Jensen transformers on the outputs that ensure distortion-free signal transfer while blocking hum and buzz from ground loops. To help retain the natural tone of your instrument, Drag control load correction is also featured on the input so you won't lose the tone and feel of connecting your guitar directly to an amplifier.

The JD7 has a built-in Radial DI box, so you can take a clean guitar track directly to your recording interface while simultaneously playing through multiple amplifiers. A Reamp® input allows you to send your recorded guitar track from your recording device back through any or all of your amps, so you can focus on the performance and have the freedom to tweak your amps and microphones later on.