But it isn’t new and others also made such amplifiers with HPF.
I personally believe SMSL have better engineering capabilities than many others but still they came up with something that others now have gone above and beyond.
Probably their next one might have HPF & LPF integration!
I think you're overestimating SMSL a bit.
Most of their devices are based on the circuit designs published by the chip manufacturers.
A few devices in their portfolio deviate completely from this and bear little to no resemblance to the circuits typically used by SMSL. With these devices, it can be assumed that the designs were developed by external developers and purchased.
Whether inexpensive or expensive devices, you often see significant cost-cutting measures on components, especially when the devices are internally developed. Even with volume and tone control ICs, they often opt for the cheaper version with limitations, as is the case here with the Rohm IC.
There are various specialized ICs that, in addition to DSP capabilities, also include high-pass and low-pass filters. Likewise, there are many inexpensive and powerful DSP ICs that cost €15 or even less than €10/$ to purchase and include good developer support from the manufacturers.
So why aren't other solutions being used?
Firstly, this is an enormous drive to cut costs at the expense of both the devices and the customers, as can be seen with some of SMSL's self-designed switching power supplies and DC/DC converters, which regularly fail, while these components from reputable and established manufacturers cost end users next to nothing.
Secondly, they simply seem to lack the necessary know-how in certain areas, as is repeatedly evident in problems, functionality, and firmware issues.
The third point appears to be a lack of knowledge, disinterest, and/or total ignorance of the functionality the market/customer requires.
Especially unsuspecting and inexperienced buyers fall into a trap because they think they are getting a great device for their application (e.g. 2.1) and in reality it is unusable for that purpose.
