It entirely depends on what you want to accomplish. The Burson op amps are FET based devices and have that rich FET like sound. I auditioned the Burson V5 op amps. While they are very resolving, they just did not sing in my system. I found myself losing interest in the music halfway into a song. It could have been because I had not upgraded the power supply at that time, but it seemed that other op amps just had more emotional engagement with me. Other people have had more positive experience. I suppose it is entirely personal taste.
The Sparkos discrete op amps are incredibly clean bipolar devices and they really sing. However, they are biased very high into Class A and the sound can become too rich/warm/slow if too many Class A stages are in the audio chain. You already have a tube output device in this DAC. If you do try Sparkos, you might end up needing to upgrade the main power supply capacitor (put larger power supply capacitors in). They do require a lot of current. These are one of my favorite op amps and I love them. They do have a large footprint, so you might have to get some additional 8-pin sockets to stack up high enough to clear those capacitors next to the op amps.
I have tried a ton of different op amps. The only other two op amps that I think are good for audio are AD797 (bipolar) and OPA827 (FET). These are mono op amps and can be mounted on a Browndog dual-adapter. You can actually buy them from Browndog already mounted, so you just need to pop them into the sockets. The OPA827 is a very nice op amp, slightly warm due to the FET inputs but it definitely has a nice magic to it. Don't buy the more expensive OPA627, as the slew rate is too high and doesn't have enough bass (everything gets a little bright/shouty). The AD797 is very neutral and is higher resolution than the OPA827. Definitely a good op amp. Not as clean sounding as Sparkos.
I really want to try the Sonic Imagery 994Enh. This is another fully discrete Class A op amp, but it doesn't have as much Class A "richness" as the Sparkos. It's more neutral/fast. It is a HUGE op amp and may not fit in all circuit boards.
Dexa is an extremely clean sounding discrete bipolar op amp. Almost like a Class D amp. Lacked emotional engagement, but good if you want an extremely clean stage.
In my testing, discrete op amps (such as Sparkos) always beat the monolithic op amps in how clean the sound was. While the monolithic op amps sounded good, they just had a dirty/messy character when compared to Sparkos/Dexa.
Probably any of these will be an upgrade to what is stock in the Music Hall DAC.
