郁而不散，必宣剂以散之，如痞满不通之类。本草云宣可去壅，生姜橘皮之属。又曰：宣者，上召下也，谓吐剂也。(考证病源, 明•刘全德撰)”

Diffusing is also used as one of the “ten formula types (shi ji 十剂),” as in diffusing formula (xuan ji 宣剂). A diffusing formula can simply mean eliminating congestion using such formulas as er chen tang.
More importantly though is noticing how Ye used the term in other places. Actually, in the constraint chapter, Ye uses diffusing (xuan) a few times and it usually appears with unblocking (tong 通) ，as in diffusing and unblocking (xuan tong 宣通)。
For example in,

diffusing and unblocking the vessels and collaterals (xuan ton mai luo 宣通脉络).

It also appears in the commentary in the phrase,

diffusing and facilitating the shao yang (xuan chang shao yang 宣畅少阳).”

There is also,

diffusing and unblocking the five constraints and six constraints (xuan tong wu yu liu yu 宣通五郁六郁).”

We can deduce by such instances, as well as the herbs used, that this diffusing does not solely relate to the Lungs.
As I post more cases that use this term diffusing we can get a better sense of what Ye is talking about and what kind of herbs he may choose for this strategy. However, at a quick glance, two medicinals that he often uses when he uses this term are yu jin or jiang huang.
However, in this case, I would not be surprised if he kept with the same idea of including medicinals such as xiang fu or shen qu. I would also assume that the tonifying aspect would simply be related to the Spleen and possibly Liver blood. Thoughts?