Connecting a speaker to AMP1 will change the sound and volume of the BluBOX's output signal. This is because the load (=speaker) at the amp's power stage significantly influences the sound, similar to tube amps. This effect isn't noticeable with a traditional tube amp, as you'd never play such an amp without a speaker cabinet.

Technically speaking, this is due to negative feedback (I-feedback), which depends on the specific impedance curve of each speaker. Each speaker has its own impedance characteristics, which influence the amp's feedback and thus change the sound and dynamics.

Many attempt to mimic the effect of the load with so-called "reactive load boxes." These devices are designed to replicate the load of the loudspeaker. However, this rarely succeeds perfectly, as the load behavior of a loudspeaker is more complex than many load boxes can reproduce.

To get close to the sound of your speaker, you can try out different load boxes available on the market and find out which one best imitates the sound of your speaker.

Another option would be to use an equalizer behind the BluBOX to compensate for the sound difference – however, you will only be able to approximate the sound; a 100% match is usually not possible.