With your splitter (either a switcher or stereo pedal), simply plug your guitar into the input of the pedal, then plug the two outputs to the input of two different amps.
Let’s talk amps
There are many different ways to run a stereo rig, but the simplest (and in my opinion best) way is to pick two amps of similar headroom – which in general will mean similar wattage. However, bear in mind that solid state and valve amps produce vastly different volume and headroom at the same power. As a rule of thumb, a valve amp of 15W or more will probably need to be paired with a solid-state amp of 50W or more.
Why wattage matters
Well as I say, it’s all about headroom – the amount of clean volume the amp produces before it starts to overdrive. This is because you ideally want to run both amps at the same volume at similar gain levels, so the sounds complement each other. This becomes especially important if you want to add gain pedals into the mix. If you decided to pair a super high-headroom 100W amp like the Victory V140 Super Duchess with a low-headroom 1W amp like a Marshall DSL-1, then the moment you stepped on a distortion pedal, the Victory with all that headroom would jump in volume, whilst the Marshall – which has far less headroom – would be pushed over the limit and would only produce more gain without a measurable increase in volume. So suddenly, your amps which were perfectly matched in volume and gain will be thrown entirely out of balance as one becomes much louder, and one is much quieter and more distorted.
Which amps pair well?
Provided your amps are roughly matched in power, this is really all down to you, and what kind of sound you’re going for. Many guitarists will pair two of the same amp, because they like that sound but they’re just looking to add more width and texture, while others will combine different amps to find their own unique tone.
A great starting point would be to try pairing any of the big 3 amp brands – Fender, Marshall and Vox. All three have their own unique characteristics that compliment each other in a variety of ways.
Perhaps the most popular combination is Fender and Marshall, famously used by Stevie Ray Vaughan and Simon Neil of Biffy Clyro. The EQs of these two amps are excellently suited to each other, as Fenders are known for their mid-scooped tone, with plenty of bass and top end sparkle, while Marshalls have a very mid-focused character that can sound very aggressive when cranked up. Together they fill in where the other lacks, so you still get the warmth and chime of the Fender, with the punch of the Marshall.