How can I start to change the system?


First of all, I must to say that I don't speak English well. So please keep that in mind. I live in Lima, Peru.

I have the following:

DVD player Rotel RDV 995 (working like an audio transport)
One Coral Cable interconnect (working like a digital cable)
DAC California Audio Labs Sigma II
AudioQuest Jaguar Interconnect
Integrated Amp Rotel RA01
AudioQuest CV6 Speaker Cables
Triangle Comette 202 Speakers

I enjoy this system a lot but I would like improve it. I was thinking about buying an tube amplifier and I wonder if I must buy another component before.

Any opinion?
osquitar
Thanks for your answers. Now I have a better idea about what I can do.

Sdcampbell: My English teacher wouldn't sign your opinion. I just noticed some big mistakes in my first post. :)

Is really important a ground connection?
Psychicanimal, please could you explain what is exactly "5) Parallel filtration for your entire system"
Thanks
ALAN
Osquitar,
I’m not sure if your original question was answered. If you purchase a tube amp you need a preamp to control the volume, unless your Integrated Amp (Rotel RA01) has the ability to be used as a preamp (it would have connectors (pins) on the back that would let you separate the amp from preamp) and run either amp or preamp separately of each other.
I do agree with Psychicanimal, the power delivery system is more important than most people realize and should be addressed.
Im agree with Swampwalker, a different digital cable would be the easiest and most cost effective way to improve your system.
Parallel filtration capacitors at the electrical panel level. Cheap and highly effective for transverse mode noise.

Both VenHaus and Igor have good solutions.