S. R. Faruqi:

shān = honor, condition, task
sārī = flowing, moving

In Urdu, akṡar means 'usually, mostly'. For example, akṡar logoñ ne samundar nahīñ dekhā hai ; or gāṛī akṡar der se ātī hai . But in its original meaning it's only 'abundance, greater part', because it's derived from kaṡīr . Thus the meaning of the first part of the first line would be 'the grandeur and dignity of passion is endlessly abundant with regard to rank and number'. Since arfāʿ is derived from rafīʿ , along with the grandeur of passion being endlessly abundant, it's also limitlessly and endlessly lofty. Here shān can also mean 'condition' or 'task'.

Another interpretation is that the grandeur and dignity of passion usually, or mostly, is endlessly lofty. In the second part of the line shān means only 'condition'. The word ʿajāʾib is extremely fine. Because in the light of Urdu idiom it evokes enchantments and astounding/marvelous things. (In fact t̤ilismāt-o-ʿajāʾib is everyday speech in Urdu.) When ʿajāʾib is used for for something in the singular, then it's taken as derived from ʿajīb . For example, baṛī ʿajāʾib jagah hai .

Now, in order to give a 'proof' that the condition of passion is extremely astounding/marvelous, in the second line he's shown two conditions that are opposite and out of the ordinary. Sometimes passion flows and moves around in the mind and heart, and sometimes it becomes judā (that is, 'different', or 'separate'). The truth is that both conditions are expressed absolutely correctly. He's composed an extremely fine verse.

FWP:

SETS
MOTIFS
NAMES
TERMS == PROOF

My translation reflects SRF's second interpretation, because it rests on the normal Urdu sense of akṡar and just generally feels better grounded to me. What I find piquant about the first line are the two occurrences of shān . Since they're divided by a 'but', we're led to think of them as somewhat contradictory or at least discrepant. And the range of meaning for shān is so wide (see the definition above) that they easily can be read as such. In my experience, the meaning of 'grandeur, glory, pomp' is more common; but Platts presents it as secondary to the more neutral sense of 'thing, affair, condition'. As so often, Mir has left us to decide for ourselves what each of the shān occurrences means, and how they fit together.

In the second line, the secondary meaning of judā as 'peculiar, extraordinary' is also enjoyable. In that sense sab se judā might become a superlative ('more extraordinary than all [others]'). Of course, in its primary sense of 'separate' it provides a wonderful effect of paradox: passion flows and circulates through everything; but it's also apart, separate, from everything, it's in a class by itself.