Yes, I was also thinking about a new M400. It seems that I have special hearing that I can hear more treble with the M400. The rest are all the same, only the M400 is different. I didn't know this until now.If you were happy with the M400, HiFi-Express is currently selling the last ones for $442.
HiFi-Express M400 442,00 USD
There are many new and used preamps on the market, but few with balanced connections.
If SE is enough for you, you can look for a cheap Sabaj A10h, relay based volume control, display and remote control for under $100. With XLR you could, for example, go for a Toppling L70, also with relay based volume control, display and remote control.
I want to try one more, the Topping DX9 with the same chip. If this is not good, then I will buy a new M400+preamp.
I have an XLR cable and the large display and the remote control are also important.
THX.