Instead of writing your second query like this:
vounum IN ('BC201203000073',
'BC201204000001',
'BC201204000002',
'BC201205000001',
'BC201206000001',
'BC201206000002')
write it like this:
vounum IN (
SELECT a.vounum
FROM actrna as a
INNER JOIN acinf as b ON a.comcod=b.comcod AND a.actcode=b.actcode
INNER JOIN sirinf as c ON a.comcod=c.comcod AND a.rescode =c.sircode
WHERE a.comcod=3305 AND a.tranam> 1000000.000000
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden