[Isis07]

It's really tough to get a full sound without hacking anything up in the ti given the speaker sizes.

I replaced the 4t's in the rear with some 6 1/2" Pioneers that were 50 bucks for a pair. I picked up the cheapest ones I could in case I messed them up fitting them. You have to hack up the 4t mounting bracket to fit them but it's not visible at all with the covering. Even $50 after market speakers were a notable improvement over the stock 4t.

I haven't replaced the 5 1/4"s in the front kick panels but I'm sure you could obtain some good replacements of the same size for under $100 (a pair).

You'll have to unsolder the wires from the current speakers and solder them onto the new speakers because BMW uses their own speaker connectors.

Could be wrong but if you want to keep it oem in appearance.. the only replacements for the door panel speakers are from Bavarian Soundwerks. They even use the stock BMW speaker connectors and fit perfectly into the stock speaker housings but they're expensive for their size. They sound cleaner but it's not worth the price for most.

Unfortunately this setup still leaves lacks lower midrange and lots of bass. I'm not a bass junkie but if you want a full sound you'll either have to put some larger speakers speakers in (that will require some sort of hacking) or get a sub. A small sub running at low power can fill in the sound very nicely without blowing out your eardrums or being clearly audible from outside of the car.

In summary... I've found a sub makes the most difference for providing a full sound but if you absolutely want to avoid that route, I'd go with replacing the 4t's in the rear with 6.5"s and the 5.25"s in the kick panel. Unfortunately I haven't messed with enough speaker brands to know which are the best for the price but as previously stated.. even the cheapest Pioneers I could find were a good improvement.