Having recently compared SEs fed with an 808v6 to some high end analogue gear, I can't say I feel you're being short changed in any way.

SE speakers fed by one of the reference endpoints is the best system I've ever heard by quite some margin. With MQA, even 5200SE produced the least 'hi-fi', most real sound I've experienced in recorded music replay.

Remember, as others have pointed out, that in a DSP setup, the 818/808 are not acting as DACs. The DACs, wideband amps, and drivers in the SEs are state of the art, and designed to work specifically with each other.

The Ultra DAC, on the other hand, might be state of the art too, but it will then meet unknown interconnect cabling, amps, and they will meet unknown speaker cabling and drivers...

HC: 861v4/ID40/LPS, DSP5000, DSP5000VC, DSP3100, SW1600, HD621, Oppo BDP-105, Sony VPL-HW55ES
2-Channel: Oppo BDP-105, TEAC VRDS-7/Trichord Clock 3/PSU, 551, Quad 303, Harbeth Compact 7ES-3, Kimber cables, Russ Andrews mains and supports.
Previous Meridian: 5000C, 5200SL, 7200.2, 6000, 562V.2, 568.2mm, 800v4, 808.2i, 818v2/v3, 861v8, 502