Keep in mind that in general in-wall speakers are poor performers compared to free-standing book shelf or others. Good-quality in-walls cost many times more than a comparably-performing regular speaker. For instance, it would probably take $5-600 for an in-wall to sound as good as a $200 bookshelf speaker. I can't imagine a $175 in-wall speaker sounding very good.
Are smallish bookshelf speakers out of the question? For $100 less that what you're looking to pay for two of these unknown inwalls, you could have a pair of the highly-regarded
SVS SBS-01 speakers. They're only 12" tall.
As for a sub, don't waste your time or money on an 8-inch sub. With few exceptions, you don't want anything less than a 12-incher.
Regards,
Wayne A. Pflughaupt