Transact SQL :: Optimize Count Distinct For Multiple Groups Of Records?

I have a CTE returning a recordset which contains a column SRC.  SRC is a number which I use later to get counts and sums for the records in a distinct list. 

declare@startdate date = '2014-04-01'
declare@enddate date = '2014-05-01'
; with SM as
(
SELECT --ROW_NUMBER() OVER (PARTITION BY u.SRC ORDER BY u.SRC) As Row,
u.SRC,

[Code] ....

-- If Referral start date is between our requested dates

ref.Referral_Start_Date between @startdate and @enddate

OR

-- Include referrals which started before our requested date, but are still active during our date range.

(ref.Referral_Start_Date < @startdate and (ref.Referral_End_Date > @startdate OR ref.Referral_End_Date IS NULL ))
)
INNER JOIN c_sdt s on s.Service_Delivery_Type_Id = u.Service_Delivery_Type_Id
AND s.Service_Delivery_Unit_Id = 200
)
SELECT
count(distinct (case SRC when 91 then client_number else 0 end)) As Eligable_91,

[code]....