Challenges with in-ear systems
Regardless of the method chosen for capturing guitar sound – whether through a microphone on the guitar cabinet, the RecOut of the AMP1, or the BluBOX – using an in-ear system requires special attention.

In-ear systems, regardless of their price, often tend to boost the highs and upper mids, which can result in a scratchy guitar tone.
When playing exclusively through in-ear monitoring, the amplifier can be set up to sound good in the headphones. However, when a guitar cabinet is used simultaneously, and the amp is adjusted for the sound through that, getting a matching sound in the in-ear headphones is rarely achieved.
Well-known bands use so-called side mixers, which are exclusively responsible for the monitor sound during a concert. Graphic equalizers, limiters, and other tools are also used to create a first-class in-ear sound.
But how can an amateur musician help himself in this situation?
The simplest solution is to insert a small mixer (ideally with parametric mids) after the BluBOX , the RecOut, or the guitar cabinet before the signal reaches the in-ear system. This allows the sound to be further adjusted in the ear (= less highs, more low mids).

If no mixer is available or if the BluBOX or RecOut is played directly into the in-ear system, you could at least insert a small EQ to reduce the scratchy frequencies a bit.

When using the BluBOX, you also have the option of changing the speakers and further adjusting the sound in the in-ear system using the mic position control.

Conclusion:
In-ear systems are becoming increasingly popular because they protect your hearing and allow you to adjust the sound to a reasonable volume. They reduce feedback problems by reducing the dependence on stage monitors, creating a clearer and more controlled listening environment.
Furthermore, these systems are constantly improving, resulting in ever-increasing sound quality. With a little practice, you can achieve excellent in-ear sounds that significantly enrich the music experience.
The following article might also be of interest to you:
How do I work with an in-ear system?