Need advice on how to dip a toe into digital

On the subject of SACD I can't comment on sound quality comparison with vinyl. I do think SACD can sound better than redbook and usually does, but I don't think that's universal. In any case, as more and more hi-rez downloads become available, it looks like SACD is becoming less and less relevant. In addition, there are audiophile redbook production methods out there (witness xrcd and the like) which to my ears can equal and may even surpass SACD sound quality. Your current player will play them just fine. Their downside is that at $30-$40 per disc they often cost more than SACDs which are high to begin with. In any event, I'd think twice before going down the SACD route at this stage of the game but, if you do then the Oppo 105 is a sensible way to go. Spending thousands on another audiophile player just to be able to play SACDs strikes me as a solution in search of a problem.

I have been using hi res files and computer since May 2010, I've experimented with quite a bit. Considering you own a PC, I agree with Gz3827 completely.... I might suggest Foobar 2000 instead of JRiver, JRiver is good, easier to use than Foobar, but once properly set up and updated to the latest software, Foobar sounds as good as JRiver.... If you don't mind spending the $50 or so, just get JRiver.
If you are not an apple head and you have enough hard drive, I'd use WAV files period, if space is a premium, then I'd look at FLAC. There are several under $500 USB DAC's that are very good...
The newest version of the Schiit BiFrost w/USB, one of the very latest Audio-Gd DAC's are excellent for the money.
Both have Asynchronous USB, at least 24/192 file capability and sound quite good for the budget.
I hope this helps,
Tim

Easy and inexpensive way to start is connect your computer to any line level input on you stereo using a stereo to dual mono RCA Y connector. I started that way and results were surprisingly good. General purpose computers are inherently noisy devices ie produce a lot of EM noise, so use a long Y connector so computer does not have to be close physically to pre-amp to connect. I've used a 12' Audioquest G-snake like this to very good effect initially before moving on to using Wifi enabled network players for a wireless digital rather than wired analog connection.

Dipping your toe won't get comparable sound quality to your current CD player or vinyl playback system.

Get the newer ARC CD9 with the built in digital inputs and match it to an Apple Mini or laptop using Pure Music or equivalent software. The downside is you won't have DSD playback.

As Grace Slick so eloquently stated, "either go away or go all the way in".

Gz... and others, thank you very much for your suggestions. I will read them a couple of times and see what I can do. Also, totally unaware of audiophile grade redbook. Where can I source such CDs and how do you know that it's audiophile grade? As I've posted elsewhere, on rare occasion I have some across some redbook CDs that are outstanding. My latest discovery is Michael Buble (Reprise).

Onhwy... excellent quote!! Btw, the newer ARC CD-9 retails for about $13K. Too steep a dive for now. I'd rather switch out my ARC VS-115 for the new ARC REF 150, the latter being a great match for my REF 5 SE. But that's ok. If you're really digitally crazy, ARC recently introduced the REF DAC for the bargain price of $16K.