Can a dolby pro logic receiver provide legacy 4 channel surround sound from a modern blu-ray...?

You will get a simulated surround effect, it may not be what the Sound studio intended, but the Dolby Logic processor will look for and attempt to extract a surround signal, in Dolby pro logic rear speakers are and were used mostly for an ambient effect to the sound coming out the front speakers, so you will get something approaching surround, not that much different than what you are experiencing already with DVD...

Yes, you will get 4 channel surround sound.

Blu-ray Disc (also known as Blu-ray or BD) is an optical disc storage medium designed by Sony to supersede the standard DVD format. Its main uses are high-definition video and data storage with 50GB per disc. The disc has the same physical dimensions as standard DVDs and CDs. The name Blu-ray Disc is derived from the blue laser (violet-colored) used to read and write to this type of disc. In part because of the shorter wavelength (405 nanometres), substantially more data (almost 6 times more) can be stored on a Blu-ray Disc than on a standard DVD, which uses a red (650 nm) laser. During the format war over high-definition optical discs, Blu-ray Disc competed with the HD DVD format. In February 2008, Toshiba—the main company supporting HD DVD— ceded and effectively ended the format war[2]. Blu-ray Disc is developed by the Blu-ray Disc Association, a group representing makers of consumer electronics, computer hardware, and motion pictures. As of January 2009, more than 890 Blu-ray disc titles are available in Australia, 720 in Japan, 1,140 in the United Kingdom, and 1,500 in the United States.[3][4][5] Contents [hide] * 1 History o 1.1 Origins o 1.2 Blu-ray Disc format finalized o 1.3 Launch and sales developments o 1.4 Competition from HD DVD o 1.5 End of the format war & future prospects * 2 Technical specifications o 2.1 Laser and optics o 2.2 Hard-coating technology o 2.3 Recording speed * 3 Software standards o 3.1 Codecs o 3.2 Java software support o 3.3 Region codes o 3.4 Digital rights management + 3.4.1 AACS + 3.4.2 BD+ + 3.4.3 BD-ROM Mark * 4 Player profiles * 5 Backward compatibility * 6 Ongoing development * 7 Variants o 7.1 Mini Blu-ray Disc o 7.2 BD9/BD5 Blu-ray Disc o 7.3 AVCREC o 7.4 Blu-ray Disc recordable * 8 See also * 9 References * 10 External links [edit] History Optical disc authoring * Optical disc * Optical disc drive * Optical disc authoring * Authoring software * Recording technologies o Recording modes o Packet writing Optical media types * Blu-ray Disc (BD): BD-R, BD-RE * DVD: DVD-R, DVD+R, DVD-R DL, DVD+R DL, DVD-RW, DVD+RW, DVD-RW DL, DVD+RW DL, DVD-RW2, DVD-RAM, DVD-D, HVD * Compact Disc (CD): Red Book, CD-ROM, CD-R, CD-RW, 5.1 Music Disc, SACD, PhotoCD, CD Video (CDV), Video CD (VCD), SVCD, CD+G, CD-Text, CD-ROM XA, CD-i * Universal Media Disc (UMD) * Holographic Versatile Disc (HVD) Discontinued Optical Disc Formats Standards * Rainbow Books * File systems * ISO 9660 * Joliet * Rock Ridge * El Torito * Apple ISO 9660 Extensions * Universal Disk Format (UDF) * Mount Rainier Further reading * History of optical storage media * High definition optical disc format war This box: view • talk • edit A blank rewritable Blu-ray Disc (BD-RE) Commercial HDTV sets began to appear in the consumer market around 1998, but there was no commonly-accepted, inexpensive way to record or play HD content. In fact, there was no medium with the storage required to accommodate HD codecs, except JVC's Digital VHS and Sony's HDCAM.[6] Nevertheless, it was well known that using lasers with shorter wavelengths would enable optical storage with higher density. When Shuji Nakamura invented practical blue laser diodes, it was a sensation, although a lengthy patent lawsuit delayed commercial introduction.[7] [edit] Origins SONY started two projects applying the new diodes: UDO (Ultra Density Optical) and DVR Blue (together with Pioneer), a format of rewritable discs which would eventually become Blu-ray Disc (more specifically, BD-RE).[8] The core technologies of the formats are essentially similar.