Adding tubes to SS system-Tube Preamp Amp or Int?

What Tgrisham said.
If you have speakers that would do well with tubes, I would recommend a tube amplifier. IMO, this is where more of the 'tube sound' comes from, but by no means is it that cut and dry.
If your speakers are designed for SS then I would recommend a tube preamplifier.

I know that for me there was no contest. The tube power amp provided the tube magic . I had tried the tube front end solutions but none of them did what the tube power amps did. Not a tube preamp, nor a tubed CD, player could came close to the effect that a tube power amp had. I understand that the real purpose of a tube buffer is to improve impedance matching and not to introduce a tube "signature" on the sonic.
Except for Micheal/Sufentenil, I am in that minority opinion but I am emphatic about that position. I am inviting your disapproval but I think anyone who has actually tried a tube power amp instead of just noting that their tube preamp made some difference would immediately realize that the tube power amp is far and away the most important factor in achieving the tube difference.
If the OP really wants to get the exaggerated droopy sluggish rolled off tubeyness typical of the unrefurbished golden age HI FI tube amps, then all he need do is buy one- for relatively little I might add. That sound is still incorrectly held by many as being the essential benefit of using tubes. It is not. The modern tube amp does not limit top end but conversely "sparkles" as my friend Trelja would say. The reason it appears to sound smoother is that it does not suffer the edgy, hashy, or gritty distortion which is more typical of SS. I am told the SS distortion is odd order whereas the tube distortion which while greater, is even order and percieved as pleasant. The real benefit however the incredible dimensionality that modern tube power amps yield, it is really 3D magic.
I agree that the tube amp bass can be looser and that low impedance highly reactive loads work well with every tube amp. Some will not be a good match with every speaker. However there are enough good speaker manufacturers aware of the popularity of tube amps that offer compatible products.
End of rant.

Mechans,
Very well said.

At least here, it does not seem to be a minority opinion that a tube power amp is the preferred way to sample tubes. I agree with that, with the caveat that it is quite important to consider power requirement as well as output impedance match. I tend to think that most people OVER estimate how much power they really need, but still, with certain speakers, one cannot consider certain amps because of power limitations. Likewise, I think a lot of people over estimate the importance of amplifier damping factor, but, there may be certain speakers with too highly reactive impedance for use with certain amplifiers.

I am a fan of low output single-ended amps (2a3, 45 tube in particular), but, frankly, these are highly specialized amps for use with high efficiency/high impedance speakers. I've also heard, and liked some higher power single-ended triode amps using 211 and 845 tubes (Wyetech and Viva amps for example), but these tend to be expensive because of the demand placed on having very high quality output transformers and power supplies. For higher power needs, my first preference are output transformerless amps, like those made by Atmasphere (very dynamic and lively sounding).

Good luck on your search. Searching for the right tube gear is either a lot of fun or a major source of frustration-it depends on your inclination to experiment, and a lot of LUCK.

I agree completely with Charles1dad, Mechans and all the rest who are advising a tube amplifier if you want to experience tubes. While upstream tubes will influence the sound of your system, they will not give your system a tube sound. In other words: tube source + tube pre + SS amp = SS sound, IMO.