What is the most difficult component to upgrade

Check out the tread on Preamp of the Century. Buy a Supratek preamp and you will be VERY HAPPY. The only downside is that you have to be very patient. This preamp is handemade one at a time in Western Australia. The wait is 4 to 6 months. It is the most musical and the most beautiful preamp I have ever encountered. You will learn a lot from the thread.

...and it has as much if not more impact on the sound as anything else in the system!

Speakers. It is very hard for me to audition them in my room with my front end. I can hear them in other systems and in other rooms but how will they sound in my room? OTOH, I can swap out a pre/amp/cdp with relative ease. It is amazing how much difference a good pre can make. I second Slowhand on the Supratek. It was worth the 6 month wait. Thanks for starting that thread Slowhand, it has forever changed my music system.
Regards,
Patrick

The front end.

For analog upgrades it is difficult to find dealers with the capability or desire to properly demonstrate different combinations.

Digital technology changes with such speed that this source has almost truly become "the flavor of the month". Then, throw in the different formats (CD, DVD-A and SACD) combined with upsampling, oversampling and combinations of formats in individual players. It makes my head spin.

I'm in the process of upgrading my digital source. For various reasons I have decided to go with a single box cd only player. I've listened to a number of players at home and in the store. I've got about $3500 available and I just can't seem to find the right one. The search goes on.......