If I made the comment about the Essence ST, it was probably with the stock opamps. I changed the opamps and it changed the sound for the better. The Essence ST and H6 has opamp sockets so you just pull the old ones off and plug in the new ones. I use the Essence ST in my work computer and have probably listened to it more over the years than just about any other soundcard at this point.
For an external multi-channel DAC, the Steinberg UR824 is the best I've used for all around home use. It has higher output voltage than consumer cards, makes no noise on turn on/off even when the amps are on, supports balanced/unbalanced output, makes no click/noise on sample rate change, supports up to 192 kHz with the firmware upgrade, allows the headphone outputs to be routed separately from the speakers, has preamps for mics with phantom power, and sounds great. They also have more frequent driver updates than what I've seen elsewhere with fast support for new OS's.
Just for fun, here are some pictures of all stuff I've had in the past 10 years:
M-Audio Revolution 7.1
Creative Labs X-Fi Elite
ASUS Essence ST with H-6 daughter board
Steinberg MR816 (Firewire)
Steinberg UR824 (USB)
Ross Martin Audio AES Eight (AES)
Solid State Logic Alpha Link (MADI) - I just had a demo unit to test before recommending it to a friend
Lynx Studio Technology Aurora 16-TB (Thunderbolt)
The picture of the Aurora 16 is actually without Thunderbolt. A Thunderbolt card for the Aurora is $595. You can also buy the Aurora with the card installed for $400 more than the standard Aurora. I bought a standard Aurora 16 and called Musicians Friend to see if I could exchange for the Thunderbolt version which was released after my purchase. I was still within 45 days of original purchase and you can return for any reason during this time. Musicians Friend said they would upgrade me to the TB version for a total of $90 and I could keep using the standard version until the new one was in stock. I ended up using the standard version for about 3 months and then shipped it back for exchange. I've always had incredible customer service with Musicians Friend.
In order to reduce circuitry in the signal path and maintain the highest levels of detail, the Ross Martin, SSL, and Lynx don't have mute circuits. For this reason, there are loud pops on turn on/off and some noise when changing sample rates. The noise on the Aurora 16-TB is barely noticeable when switching sample rates, though. It is much quieter through Thunderbolt than AES for some reason. These 3 DACs also all have adjustable output voltage which can be helpful when using EQ or convolution and need to increase the output voltage. Or you might want lower voltage for sensitive speakers.