This is how I listen to my RAAL SR1a and CA-1a. I used to use a RAAL VM-1a dedicated RAAL tube amp for this and it is the best for these phones. However, I needed the cash so I sold that amp and got the following cheaper gear,
Schitt Aegir amp | Schitt Mjolnir preamp | DAC | RAAL TI-1b 2-channel amp adapter
The reason I was able to sell the VM-1a was because the new TI-1b adapter gets you to about 90% of the level of the VM-1a.
Well what if you do not have the RAAL SR1a or CA-1a. That is a mistake and you should test drive my 2 phones to see if it is even better than your 2-channel. The SR1a is similar to 2-channel and the CA-1a has a traditional headphone sound.
BTW - the Schiit preamp I mention above is a headphone amp/preamp and I used it as a preamp, the headphone amp part is too weak for my RAALs.