Find the next letter cluster in the given series:
$\text{DA},\text{HE},\text{NK},\text{RO},\text{XU},\_\_\_\_\_\_\_\_\_\_\_$

Let's split the elements into individual positional tracking groups:
* First Letters: $\text{D}(4)\stackrel{+4}{\to }\text{H}(8)\stackrel{+6}{\to }\text{N}(14)\stackrel{+4}{\to }\text{R}(18)\stackrel{+6}{\to }\text{X}(24)$
The step alternates between adding $4$ and $6$. The next increment must be $+4$:

$$24+4=28\equiv 2\to \text{B}$$

* Second Letters: $\text{A}(1)\stackrel{+4}{\to }\text{E}(5)\stackrel{+6}{\to }\text{K}(11)\stackrel{+4}{\to }\text{O}(15)\stackrel{+6}{\to }\text{U}(21)$
The step alternates identically ($+4,+6$). The next increment must be $+4$:

$$21+4=25\to \text{Y}$$

Combining both values gives the cluster $\text{BY}$.