it not sounding as good as the blows (Bose) unit makes sense as blows spends time and money trying to engineer a sound that is not necessarily accurate, but IS pleasing to the ear. The hertz speakers shouldnt sound like theyre in a tube tho. Your issue could be a crossover or time alignment setting. In either event, the car audio shop should have probably stuck with replacing the tweeters in the a pillars as it would have brought the sound stage up and rounded out the frequency response quite a lot. One thing that blows(i will be referring to Bose as blows for the duration of this response )has in its advantage is that it has outboard amplifiers it utilizes instead of deck power. In addition to that, the stock speakers you replaced were specifically designed to run on the power from the stock deck and the stock deck wont run a pair upgraded speakers very well. Since you upgraded the deck , you should have a bump in power going to the speakers, but its still not ideal for non stock speakers. That being said, it shouldnt sound like its in a tunnel. You really should get an amp, and you should strongly consider getting some pillar tweeters. You honestly can get by with a inexpensive amp that will put out some real usable power and still be reliable. as far as tweeters, youre gonna be stuck with either upgrading to components that have an external passive crossover or, you could take advantage of this misfortune and go with an active crossover setup amplifying your tweeters and mid drivers separately. If you just get a 4 channel amp and a pair of tweeters and go active, itll literally blow your mind.
parts are less than $150 and youll need some wiring, but those two will get you set to go