Using a guitar amp with your Boss GT-10 or GT-8

Using the overdrive effect without a preamp model 

Of course you can use the Boss GT-8 or GT-10 like every other multi-effect device from the '90th. Connect it to a clean guitar amp and only use the available overdrive and distortion models, but not the preamp models. With 30 different overdrive and distortion models - in the '90th I had an Ibanez PT3DX with 6 overdrive/distortion models - you should be able to get every needed sound from blues to rock to metal. Important is that your amp has a good sounding clean channel. Fine tuning can be done with the Boss GT EQ and/or the FX1 tone modify modul.
Everyone who claims that you need an overdriven tube amp in order to get a good distorted sound, should think about the old rockers of the '70th and '80th. They didn't have a Rectifier or 5150. Instead of, they used a clean or crunchy Fender, Vox or Marshall amp with an overdrive/distortion pedal! Don't try to imitate a Rectifier with the preamp models of the boss gt-8 or gt-10 through a Fender amp! It won't work.
Use the overdrive and distortion models of the Boss GT-10 and get your sound with a clean amp.

This will give you a prominent sound which can set standards. And it's much better than imitating the PRS Rectifier sound everywhere used in modern music.

What did I want to tell you? Using the Boss GT-10 or GT-8 with a guitar amp is possible and can give you surprisingly good sounds. But don't use the preamp models with a real guitar amp when connecting to the normal guitar input.

Use the Boss GT-10 / GT-8 like your old stompboxes.

Using the preamp effect

You can use the preamp effect with your guitar amp, but then you should bypass the build in preamp of your guitar amp. Therefore connect the Boss GT-10 / GT-8 to the effects return of your amp. This is done because the preamp colors your sound and you don't want to get the sound of your amp but the sound of the Boss GT. Your amp will still color the sound because a 1 x 12" combo speaker can't sound like a 8 x 12" stack. But if you use an amp suitable for your music then e.g. you will get a sound close to a Rectifier from your Marshall stack. It's even possible to get a descent clean sound from your Rectifier using a clean preamp of the Boss GT.