Best Classical to "broaden" listening arena?

Among the composers who IMO should be on your initial short list, I would add Schubert, Chopin, Dvorak, and Schumann to those already suggested in Ojgalli's post. If opera may be of interest, Puccini. From the earlier Baroque period, Telemann and Handel. And for some fun stuff, that can often show off a high quality system to good advantage, try some music from the even earlier Renaissance period.

I would also suggest giving preference to recordings produced on labels that are recognized for consistently good sound quality. A lot of excellent musical material that has been put out over the years by the major labels is sonically ruined by excessive multi-mic'ing and processing, which may prove to be particularly discouraging during your initial explorations.

I have found the following labels to have provided excellent sounding recordings with a high degree of consistency, although unfortunately a number of them no longer exist:

Accent
Astree
Audiofon
Chesky
Dorian
Harmonia Mundi France
Hyperion
Lyrinx
M&K Realtime
Mercury Living Presence re-issues
North Star
Pierre Verany
Proprius
Reference Recordings
Sheffield Labs
Syrinx
Telarc (many are excellent; some will be disappointing)
Valois
Wilson Audio

Enjoy!

-- Al