I think
@Bengkia369's explanation is easier with pictures.
He recommends the Trulis 8802 for a tuby sound. I can confirm. It's more analog, the bass is slightly rounded, the stage is wider. A warmth and bloom to the presentation. The resolution and sterility of the ESS dac will take a hit.
The MK08 with 8802. You will be able to fit in with the door closed. The 8802 comes with a dip8 leg. If you use the leg. It will become too high to close the door. So you need to stick it in directly if you intend to use the MK08. Pic below.
Do you need the UFEEL adapters? No. They're buffers, adding capacitors to enhance the sound. Both the UFEEL, I find they work. The MK09 is a pretty dramatic change. Micro nuances can be imagined. Pushing the mids forward in the overall presentation is obvious. I find the MK08 subtle. MK09 is very obvious. The Burson V7V is dead neutral. A bit boring. The MK09 pushes the mids forward, making the presentation more musical with no hit to the micro details from what I can hear.
If you look closely at the MK09. You will see a MK08 soldered on. There is no need to buy both. If you are going to buy. Make sure you choose the AG and Dual version.
The MK09 will not fit even with the door closed. You will need flexible leg extensions. Pic below.
8802 directly in the MK08. This setup will fit with the door closed.
MK09 will not fit the amp board directly. The width is too wide.
MK09 with leg extensions. In this method, you can use any sized opamps. Including the excellent Burson V7, or the Sparkos something something (sorry cannot recall at the moment). Of course, the transportable option is now more limited. The upside. You can change opamps easily. I only use it in the house and mostly at my desk. So this is fine for me.