You don't indicate if you have a budget, or if you want to undertake the conversion to 2-channel in stages. More information about your plans would help forum members to provide you with appropriate suggestions.
By way of introducion, I should tell you that I share your bias toward 2-channel, but I also enjoy HT on occasion. I tried to build my own system so it offered first-rate 2-channel sound, but also did a good job with HT. On the whole, I think my system does a fine job with both formats. (For specific info about the components I own, my system is listed in "Virtual Systems" - see link below).
There are two schools of thought about where to start on a good audio system. One group says start at the source end of the chain (CD player, turntable, etc.), while the other group tends to focus more on the amplifier/speaker chain. I personally think that there are no longer great differences between a good analog vs. good digital source, and the audio quality differences between CD players have narrowed considerably over the past 5 years. Further, putting aside the debate over the merits of SACD vs. DVD-A, I think that the differences between CD players in a given price range, and SACD/DVD-A players in the same price bracket, are pretty minor.
As a generalization, I'd suggest you initiate the changes in your system in the following order: speakers, then preamp, and then amp. In my personal opinion (based on about 40 years as an audio buff), speakers make the greatest difference of any component in your system, so start there. In most audio systems today (assuming the person does not have a turntable system), the speaker is the only transducer in the signal path. Transducers convert electrical energy into mechanical energy (or vice versa, in the case of a phono cartridge), and are subject to non-linearities that can really degrade sound quality. Hence, you want a transducer that converts the signal with as little distortion as possible. Furthermore, speakers are usually based on the listening biases of the designer, with the end result often being rather subjective. (IMO, too many "audiophile" speakers have problems, such as lack of flat frequency response, lack of time and phase accuracy, etc.)
Next in order is the preamp. The preamp must take signals with very low voltages and amplify them before the amp adds the juice needed to drive the speakers. These low voltage signals must be amplified VERY accurately, which requires a very good electrical design. Flat frequency response, for example, is absolutely critical in a good preamp. There are some differences between the "sound" of a tube preamp vs. a solid state preamp, although the best preamps of either type are very neutral. Your choice of tube vs. solid state may be dictated somewhat by your own listening tastes, so you may want to audition a good example of both tube and solid state preamp before making a final choice.
The final item in the chain is the amplifier. There are a lot of good amps on the market today, both solid state and tube. The choice of amplification method (transistors vs. tubes) is a matter of personal choice -- I've owned both, sold both, and personally think that solid state amps make the most sense today (that sound you hear is the howls of protest from tube amp owners). So, the objective in selecting a power amp is to find one that is most compatible with your speakers. Most speakers (again, a generalization) that have relatively low nominal impedances (say, down to about 3-4 ohms) will perform better with a solid state amp that is capable of delivering good current and good damping at lower impedances. Speakers with relatively high nominal impedances (say, 12 ohms) are more compatible with tube amps, which generally work better with high impedances. Ultimately, you need to audition the amplifier with the speakers you decide to buy -- and do so in your home if at all possible.
I'll conclude my input by returning to your remark that you want a "warm and musical system". Given that, you should look at the Vandersteen 3A Signatures or the Vandersteen Model 5's, depending on the size of your budget. As you will note from looking at my system, I own Vandersteen speakers, and think they not only make wonderful music, but are great for HT and offer excellent value as well. Even if you decide to buy a different speaker brand, the Vandies should be on your short list given your listening desires.
After you have made these major changes to your system, you can worry about getting a newer CD/SACD player, or doing some fine tuning with different interconnects or speaker cables. But that's a whole new thread...
