Shouldn't Filter #6 be the best filter to use: described as "Linear Fast Roll-off" on their website:
Foshan ShuangMuSanLin electronics Co., LTD. founded in 2009 which located in Shenzhen, China. And our branch company VMV Technology(HK) Company Limited registered in HK in 2013. Our company is specialized in the audio DAC, stereo headphone amplifier, power amplifier, and with own R&D...
www.smsl-audio.com
Linear Fast Roll-off is normally associated with the best filter from a technical perspective.
Following the graph of filters for this DAC, I'm pretty sure Filter #6 is the best filter to use as historically viewed here on ASR:
In above graph you can see filter #6 (pink filter) is -10dB down at 22kHz and at -100dB at 24kHz which is also the same as the Sharp Filter in the Topping E30 seen in the following graph which is the recommended filter for the E30:
So Filter #6 should be the best filter for the SMSL DO100 and Filter #1 should be the best Filter for the Topping E30 - both filters are identical - Linear Fast Roll Off.
(
@amirm , worth retesting some relevant parts with Filter #6 on the SMSL DO100?)