How much $$ we talkin' about?
A lot=3,000$
Obscene=10,000$
Profane=60,000$
For 'A lot' of money I'd work on the room. Acoustic treatments, new drapes and other appearance items.
At the 'Obscene' level, I'd add some new electronics and a pair of new subs, to replace the single sub I now have.
If I were truly 'Profane', I'd go all the way spend and about 130$ per square foot on a full designed in room addition of about 300 ft/sq. At that point, I'd replace my MG1.6s with the forthcoming (I should live so long!) MG3.7s