Since we are confronted with this misunderstanding quite often, the answer comes here in big and bold letters:

The BluBOX cannot change the sound of the guitar speaker cabinet connected to the THRU!

The speaker simulation of the BluBOX is available at the BALANCED MIC OUT and the LINE OUT. From there it can be connected to a full-range (!) active speaker (e.g. a monitor, etc.), to a mixer, DAW or headphones. Both connections can be assigned and used at the same time. The BluBOX virtually replaces the microphone-mounted guitar cabinet.

The emulated signal is not meant to be passed on to a guitar cabinet! Doing so would not work at all. In order to reproduce the speaker simulations of the BluBOX as true to the original as possible, the emulated signal must be processed and outputted neutrally. Therefore, it is recommended to connect it to a sound-neutral full-range speaker, mixer, interface, etc..

A guitar cabinet has its own unique sound character, which significantly colors and, in a way, "alters" the incoming signal. The BluBOX is designed to accurately capture these individual characteristics of various guitar cabinets. Consequently, sending the emulated signal from the BluBOX to a guitar cabinet would be impractical, as it would be akin to placing a microphone in front of one guitar cabinet and then connecting that microphone to another guitar cabinet.

The unprocessed signal that arrives at the SPEAKER LEVEL IN is present at the THRU of the BluBOX. This connection is used to route the SPEAKER OUT signal from the amplifier to a guitar cabinet without any processing.

In other words: the BluBOX is designed to simulate 16 different loudspeaker cabs and then connect them to the mixer. This eliminates the need for miking the guitar cab, and it even allows you to play without a physical cab. Additionally, you gain the advantage of having not just one (your own) cabinet but 16 different cabs to choose from. However, if you still wish to connect your own guitar cabinet, you can do so using the THRU output, which provides the unprocessed input signal.