OP, do not be led to believe there is anything wrong with your hearing or impressions. You are not the first to report hearing zero difference between servers. I suspect many owners of high cost "audiophile" servers will denounce such a finding as nonsense.
I have long been skeptical of high-end servers. Some claim to use custom motherboards, but most use off-the-shelf processors from AMD and Intel. Their proprietary operating systems are touted, but most are based off Linux. I also see a lack of accommodation for upsampling, which requires a lot of processing power. Most servers are simply not powerful enough to do upsampling, at least beyond DSD128. Support for software like HQPlayer is also lacking.
If one is willing to do DIY approach, a SOTA server can be built for fractions of the cost. Take a Mac Mini or Intel NUC, boot it from Audiolinux (which has native support for Roon and HQPlayer), add a LPS, and connect it to your network with ethernet.