In general, I would say that keeping the low frequencies separate from small bookshelf speakers is the best way to go. An 8" or 10" inch speaker in a small box will not compete with a dedicated sub. I would get "cheaper speakers" that do the upper bass, midrange and highs well and spend the savings on a good sub. For good bass, the bigger the enclosure is better. That's why SVS builds water heaters and the EP600 is so tall. Just my $0.02.